Coated porous substrates

ABSTRACT

A coated porous substrate comprising a porous substrate having a coating of electrically conductive tin oxide on at least a portion of all three dimensions thereof. The coated porous substrate is useful in the lead acid batteries, catalysis, heating, shielding porous membrane and field dependent fluid applications.

RELATED APPLICATIONS

This application is a continuation in part application of applicationSer. No. 08/293,699 filed Aug. 19, 1994 and 07/874,178 filed Apr. 24,1992 now abandoned said first application Ser. No. 08/293,699 is adivisional application of Ser. No. 07/874,178 which application Ser. No.07/874, 178 is a continuation in part of application Ser. No. 770,557,filed Oct. 3, 1991 now abandoned, which application is a continuation inpart of application Ser. No. 621,660 filed Dec. 3, 1990 now U.S. Pat.No. 5,204,140 which application in turn is a continuation-in-part ofapplication Ser. Nos. 348,789 now U.S. Pat. No. 5,167,820; 348,788 nowU.S. Pat. No. 5,039,845; 348,787 now abandoned and 348,786 now U.S. Pat.No. 5,182,165 each filed May 8, 1989, each of which applications is acontinuation-in-part of application Ser. Nos. 272,517 and 272,539, eachfiled Nov. 17, 1988, each now abandoned each of which application inturn, is a continuation-in-part of application Ser. No. 082,277, filedAug. 6, 1987 (now U.S. Pat. No. 4,787,125) which application, in turn,is a division of application Ser. No. 843,047, filed Mar. 24, 1986, nowU.S. Pat. No. 4,713,306. Each of these earlier filed applications andthese U.S. Patents are incorporated in its entirety herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a process for coating a substrate. Moreparticularly, the invention relates to coating a substrate with a tinoxide-containing material, preferably an electrically conductive tinoxide-containing material and to coated porous substrates.

An application where substrates with coatings, e.g., electricallyconductive coatings, find particular usefulness is in the promotion ofchemical reactions, e.g., gas/liquid phase reactions, electro catalyticreactions, photo catalytic reactions, redox reactions, etc. As anexample of a type of reaction system, a catalytic, e.g., metallic,component is contacted with the material to be reacted, e.g.,hydrocarbon, carbon monoxide is passed through or near to the catalyticcomponent to enhance the chemical reaction, e.g., hydrocarbon, carbonmonoxide oxidation to carbon dioxide and water and nitrogen oxidereduction to nitrogen. In addition, using a substrate for the catalyticcomponent which is coated with an electrically conductive material ishighly advantageous for electro and photoelectron catalysis and/or rapidheat transfer to catalyst surfaces since a field/current can beeffectively and efficiently provided to or near the catalytic componentfor electron transfer reactions. Many types of chemical reactions can beadvantageously promoted using such coated substrates. Tin oxidecontaining coatings on substrates may promote a electron transferwhether or not the chemical reaction is conducted in the presence of aelectro photo electro current or field. In addition, tin oxide coatedsubstrates and sintered tin dioxides are useful as gas sensors, andcombustion type devices and articles. One or more other components,me.g., metal components, are often included in certain of theseapplications.

In many of the above-noted applications it would be advantageous to havean electrically, electronically conductive; electro mechanical tin oxidewhich is substantially uniform, has high electronic conductivity, andhas good chemical properties, e.g., morphology, stability, etc.

A number of techniques may be employed to provide conductive tin oxidecoatings on substrates. For example, the chemical vapor deposition (CVD)process may be employed. This process comprises contacting a substratewith a vaporous composition comprising a tin component and adopant-containing material and contacting the contacted substrate withan oxygen-containing vaporous medium at conditions effective to form thedoped tin oxide coating on the substrate. Conventionally, the CVDprocess occurs simultaneously at high temperatures at very short contacttimes so that tin oxide is initially deposited on the substrate. Howevertin oxide can form off the substrate resulting in a low reagent capturerate. The CVD process is well known in the art for coating a single flatsurface which is maintained in a fixed position during the above-notedcontacting steps. The conventional CVD process is an example of a"line-of-sight" process or a "two dimensional" process in which the tinoxide is formed only on that portion of the substrate directly in thepath of the tin source as tin oxide is formed on the substrate. Portionsof the substrate, particularly internal surfaces, which are shieldedfrom the tin oxide being formed, e.g., such as pores which extendinwardly from the external surface and substrate layers which areinternal at least partially shielded from the depositing tin oxidesource by one or more other layers or surfaces closer to the externalsubstrate surface being coated, do not get uniformly coated, if at all,in a "line-of-sight" process. Such shielded substrate portions eitherare not being contacted by the tin source during line-of-sightprocessing or are being contacted, if at all, not uniformly by the tinsource during line-of-sight processing. A particular problem with"line-of-sight" processes is the need to maintain a fixed distancebetween the tin source and the substrate. Otherwise, tin dioxide can bedeposited or formed off the substrate and lost, with a correspondingloss in process and reagent efficiency.

One of the preferred substrates for use as catalysts including use as acatalyst additive in batteries, such as the positive active material oflead-acid batteries, are inorganic substrates, in particular flakes,spheres, fibers and other type particles. Although the CVD process isuseful for coating a single flat surface, for the reasons noted abovethis process tends to produce non-uniform and/or discontinuous coatingson non-flat, non-equidistant surfaces and/or three dimensional surfaceshaving inner shielded surfaces and/or the processing is multi-stepand/or complex and/or time consuming. Such non uniformities and/ordiscontinuities and/or processing deficiencies are detrimental to theelectrical and chemical properties of the coated substrate. A newprocess, e.g., a "non-line-of-sight" or "three dimensional" process,useful for coating such substrates would be advantageous. As usedherein, a "non-line-of-sight" or "three dimensional" process is aprocess which coats surfaces of a substrate with tin oxide whichsurfaces would not be directly exposed to tin oxide-forming compoundsbeing deposited on the external surface of the substrate during thefirst contacting step and/or to improve the processability to conductivecomponents and articles and/or for the type of substrate to be coated.In other words, a "three dimensional" process coats coatable substratesurfaces which are at least partially shielded by other portions of thesubstrate which are closer to the external surface of the substrateand/or which are further from the tin oxide forming source duringprocessing, e.g., the internal and/or opposite side surfaces of a glassor ceramic fiber or spheres, or flakes or other shapes or surfaces.

Although a substantial amount of work has been done, there continues tobe a need for a new method for coating substrates, particularly threedimensional substrates with tin oxides. The prior art processesdescribed below follow conventional processing techniques such as bysintering of a tin oxide and/or the instantaneous conversion to tinoxide by spray pyrolysis.

For example in "Preparation of Thick Crystalline Films of Tin Oxide andPorous Glass Partially Filled with Tin Oxide," R. G. Bartholomew et al,J. Electrochem, Soc. Vol. 116, No. 9, p1205(1969), a method is describedfor producing films of SnO₂ on a 96% silica glass substrate by oxidationof stannous chloride. The plates of glass are pretreated to removemoisture, and the entire coating process appears to have been done underanhydrous conditions. Specific electrical resistivity values for SnO₂-porous glass were surprisingly high. In addition, doping with SbCl₃ wasattempted, but substantially no improvement, i.e., reduction, inelectrical resistivity was observed. Apparently, no effective amount ofantimony was incorporated. No other dopant materials were disclosed.

In "Physical Properties of Tin Oxide Films Deposited by Oxidation ofSnCl₂," by N. Srinivasa Murty et al, Thin Solid Films, 92(1982) 347-354,a method for depositing SnO₂ films was disclosed which involvedcontacting a substrate with a combined vapor of SnCl₂ and oxygen.Although no dopants were used, dopant elements such as antimony andfluorine were postulated as being useful to reduce the electricalresistivity of the SnO₂ films.

This last described method is somewhat similar to the conventional spraypyrolysis technique for coating substrates. In the spray pyrolysisapproach tin chloride dissolved in water at low pH is sprayed onto ahot, i.e., on the order of about 600° C., surface in the presence of anoxidizing vapor, e.g., air. The tin chloride is immediately converted,e.g., by hydrolysis and/or oxidation, to SnO₂, which forms a film on thesurface. In order to get a sufficient SnO₂ coating on a glass fibersubstrate to allow the coated substrate to be useful as a component of alead-acid battery, on the order of about 20 spraying passes on each sidehave been required. In other words, it is frequently difficult, if notimpossible, with spray pyrolysis to achieve the requisite thickness anduniformity of the tin oxide coating on substrates, in particular threedimensional substrates.

Dislich, et al U.S. Pat. No. 4,229,491 discloses a process for producingcadmium stannate layers on a glass substrate. The process involveddipping the substrate into an alcoholic solution of a reaction productcontaining cadmium and tin; withdrawing the substrate form the solutionin a humid atmosphere; and gradually heating the coated substrate to650° C. whereby hydrolysis and pyrolysis remove residues from the coatedsubstrate. Dislich, et al is not concerned with coating substrates forlead-acid batteries, let alone the stability required, and is notconcerned with maintaining a suitable concentration of a volatiledopant, such as fluoride, in the coating composition during productionof the coated substrate.

Pytlewski U.S. Pat. No. 4,229,491 discloses changing the surfacecharacteristics of a substrate surface, e.g., glass pane, by coating thesurface with a tin-containing polymer. These polymers, which may containa second metal such as iron, cobalt, nickel, bismuth, lead, titanium,canadium, chromium, copper, molybdenum, antimony and tungsten, areprepared in the form of a colloidal dispersion of the polymer in water.Pytlewski discloses that such polymers, when coated on glass surfaces,retard soiling. Pytlewski is not concerned with the electricalproperties of the polymers or of the coated substrate surfaces.

Gonzalez-Oliver, C. J. R. and Kato, I. in "Sn (Sb)-Oxide Sol-GelCoatings of Glass," Journal of Non-Crystalline Solids 82(1986) 400-410North Holland, Amsterdam, describe a process for applying anelectrically conductive coating to glass substrates with solutionscontaining tin and antimony. This coating is applied by repeatedlydipping the substrate into the solution of repeatedly spraying thesolution onto the substrate. After each dipping or spraying, the coatedsubstrate is subjected to elevated temperatures on the order to 550°C.-600° C. to fully condense the most recently applied layer. Otherworkers, eg., R. Pryane and I. Kato, have disclosed coating glasssubstrates, such as electrodes, with doped tin oxide materials. Theglass substrate is dipped into solution containing organo-metalliccompounds of tin and antimony. Although multiple dippings are disclosed,after each dipping the coated substrate is treated at temperaturesbetween 500° C. and 630° C. to finish off the polycondensationreactions, particularly to remove deleterious carbon, as well as toincrease the hardness and density of the coating.

SUMMARY OF THE INVENTION

A new process for at least partially coating a substrate with a tinoxide-forming material has been discovered. In brief, the processcomprises contacting the substrate with a tin oxide precursor, forexample, stannous chloride, in a vaporous form and/or in a liquid formand/or in a solid (e.g., powder) form, to form a tin oxideprecursor-containing coating, for example, a stannouschloride-containing coating, on the substrate; preferably contacting thesubstrate with a fluorine component, i.e., a component containing freefluorine and/or combined fluorine (as in a compound), to form a fluorinecomponent-containing coating on the substrate; and contacting the coatedsubstrate with an oxidizing agent to form a tin oxide-containing,preferably tin dioxide-containing, coating on the substrate. Thecontacting of the substrate with the tin oxide precursor and with thefluorine component can occur together, i.e., simultaneously, and/or inseparate steps.

This process can provide coated substrates which have substantialelectrical conductivity so as to be suitable for use as components inbatteries, such as lead-acid storage batteries. Substantial coatinguniformity, e.g., in the thickness of the tin oxide-containing coatingand in the distribution of dopant component in the coating, is obtained.Further, the present fluorine or fluoride doped tin oxide coatedsubstrates have outstanding stability, e.g., in terms of electricalproperties and morphology, and are thus useful in various applications.In addition, the process is efficient in utilizing the materials whichare employed to form the coated substrate.

DETAILED DESCRIPTION OF THE INVENTION

In one broad aspect, the present coating process comprises contacting asubstrate with a composition comprising a tin oxide precursor, such astin chloride forming components, including stannic chloride, stannouschloride, tin complexes and mixtures thereof, preferably stannouschloride, at conditions, preferably substantially non-deleteriousoxidizing conditions, more preferably in a substantially inertenvironment or atmosphere, effective to form a tin oxideprecursor-containing coating, such as a stannous chloride-containingcoating, on at least a portion of the substrate. The substrate ispreferably also contacted with at least one dopant-forming component,such as at least one fluorine component, at conditions, preferablysubstantially non-deleterious oxidizing conditions, more preferably in asubstantially inert atmosphere, effective to form a dopant-formingcomponent-containing coating, such as a fluorine component-containingcoating, on at least a portion of the substrate. This substrate,including one or more coatings containing tin oxide precursor, forexample tin chloride and preferably stannous chloride, and preferably adopant-forming component, for example a fluorine component, is contactedwith at least one oxidizing agent at conditions effective to convert thetin oxide precursor to tin oxide and form a tin oxide-containing,preferably tin dioxide-containing, coating, preferably a doped, e.g.,fluorine or fluoride doped, tin oxide-containing coating, on at least aportion of the substrate. By "non-deleterious oxidation" is meant thatthe majority of the oxidation of tin oxide precursor, for examplestannous chloride, coated onto the substrate takes place in theoxidizing agent contacting step of the process after distribution and/orequilibration of the precursor, rather than in process step or stepsconducted at non-deleterious oxidizing conditions. The process as setforth below will be described in many instances with reference tostannous chloride, which has been found to provide particularlyoutstanding process and product properties. However, it is to beunderstood that other suitable tin oxide precursors are included withinthe scope of the present invention.

The dopant-forming component-containing coating may be applied to thesubstrate before and/or after and/or during the time the substrate iscoated with stannous chloride. In a particularly useful embodiment, thestannous chloride and the dopant-forming component are both present inthe same composition used to contact the substrate so that the stannouschloride-containing coating further contains the dopant-formingcomponent. This embodiment provides processing efficiencies since thenumber of process steps is reduced (relative to separately coating thesubstrate with stannous chloride and dopant-forming component). Inaddition, the relative amount of stannous chloride and dopant-formingcomponent used to coat the substrate can be effectively controlled inthis "single coating composition" embodiment of the present invention.

In another useful embodiment, the substrate with the stannouschloride-containing coating and the dopant-forming component-containingcoating is maintained at conditions, preferably at substantiallynon-deleterious oxidizing conditions, for example, conditions whichreduce and/or minimize the formation of tin oxide on a relatively smallportion of the substrate or off the substrate, for a period of timeeffective to do at least one of the following: (1) coat a larger portionof the substrate with stannous chloride-containing coating; (2)distribute the stannous chloride coating over the substrate; (3) makethe stannous chloride-containing coating more uniform in thickness; and(4) distribute the dopant-forming component more uniformly in thestannous chloride-containing coating. Such maintaining preferably occursfor a period of time in the range of about 0.05 or 0.1 minute to about20 minutes in the presence of an inert gas an/or oxygen i.e. air, undernon-deleterious oxidizing conditions. Such maintaining is preferablyconducted at the same or a higher temperature relative to thetemperature at which the substrate/stannous chloride-containingcomposition contacting occurs. Such maintaining, in general, acts tomake the coating more uniform and, thereby, for example, provides forbeneficial electrical conductivity properties. The thickness of the tinoxide-containing coating is preferably in the range of about 0.1 micronto about 10 microns, more preferably about 0.25 micron to about 1.25microns.

In another useful embodiment, the coating process comprises contacting aporous substrate, particularly, porous particle substrates with acomposition comprising a tin oxide precursor at conditions, preferablysubstantially non-deleterious oxidizing conditions, effective to form atin oxide precursor containing coating such as a stannous chloridecontaining coating, preferentially, on the outer surface of thesubstrate preferably a majority of the outer surface while limitingand/or controlling differentially to the outer surface the coating ofthe open internal pore surface of said substrate. The substrateincluding one or more coatings containing tin oxide precursor andpreferably a dopant forming component, for example, a fluorine componentis contacted with at least one oxidizing agent at conditions effectiveto convert the tin oxide precursor to tin oxide and form a tin oxidecontaining, preferably tin dioxide containing coating, preferably adoped, e.g., fluorine or fluoride doped tin oxide containing coating,preferentially, on the outer surface of the substrate while limitingand/or controlling the amount of coating in the internal pores of thesubstrate. In general, the outer surface is the surface that wouldcontact the surface of another particle of similar size and geometry byfor example forming a conductive electrical contact between such outersurfaces. As set forth above, it is preferred to have a majority of suchouter surfaces on an area basis coated, more preferably greater thanabout 70% and still more preferably, greater than about 90% of suchouter surface. In general, the coating of the open internal poroussurfaces is controlled and/or limited to provide a non-coated internalsurface, preferably to provide at least about 10% non-coated internalsurface on an internal surface area basis, more preferably, at leastabout 30%, still more preferably, at least about 50% and still morepreferably, at least about 70% non-coated internal surfaces. The processfor preferentially coating the substrate outer surface while limitingthe coating in the internal pores and surfaces of the substrate providesunique and unexpected properties in many various applications,particularly, in lead acid battery, resistance resistant heating,catalysis and shielding applications.

The stannous chloride which is contacted with the substrate is in avaporous phase or state, or in a liquid phase or state, or in a solidstate or phase (powder) at the time of the contacting. The compositionwhich includes the stannous chloride preferably also includes thedopant-forming component or components. This composition may alsoinclude one or more other materials, e.g., dopants, catalysts, graingrowth inhibitors, solvents, etc., which do not substantially adverselypromote the premature hydrolysis and/or oxidation of the stannouschloride and/or the dopant-forming component, and do not substantiallyadversely affect the properties of the final product, such as by leavinga detrimental residue in the final product prior to the formation of thetin oxide-containing coating. Thus, it has been found to be important,e.g., to obtaining a tin oxide coating with good structural, mechanicaland/or electronic properties, that undue hydrolysis of the tin chlorideand dopant-forming component be avoided. This is contrary to certain ofthe prior art which actively utilized the simultaneous hydrolysisreaction as an approach to form the final coating. Examples of usefulother materials include organic components such as acetonitrile, ethylacetate, dimethyl sulfoxide, propylene carbonate and mixtures thereof;certain inorganic salts and mixtures thereof. These other materials,which are preferably substantially anhydrous, may often be considered asa carrier, e.g., solvent, for the tin chloride and/or dopant-formingcomponent to be contacted with the substrate. It has also been foundthat the substrate can first be contacted with a tin oxide precursorpowder, particularly stannous chloride powder, preferably with a filmforming amount of such powder, followed by increasing the temperature ofthe powder to the liquidous point of the powder on the substrate andmaintaining the coated substrate for a period of time at conditionsincluding the increased temperature effective to do at least one of thefollowing: (1) coat a larger portion of the substrate with the tin oxideprecursor-containing coating; (2) distribute the coating over thesubstrate; and (3) make the coating more uniform in thickness.Preferably, this step provides for the equilibration of the coating onthe substrate. The size distribution of the powder, for example, tinchloride powder, and the amount of such powder applied to the substrateare preferably chosen so as to distribute the coating over substantiallythe entire substrate.

The tin oxide precursor powder can be applied to the substrate as apowder, particularly in the range of about 5 or about 10 to about 125microns in average particle size the size in part being a function ofthe particle size, i.e. smaller particles generally require smaller sizepowders. The powder is preferably applied as a charged fluidized powder,in particular having a charge opposite that of the substrate or at atemperature where the powder contacts and adheres to the substrate. Incarrying out the powder coating, the coating system can be, for example,one or more electrostatic fluidized beds, spray systems having afluidized chamber, and other means for applying powder, preferably in afilm forming amount. The amount of powder used is generally based on thethickness of the desired coating and incidental losses that may occurduring processing. The powder process together with conversion to a tinoxide-containing coating can be repeated to achieve desired coatingproperties, such as desired gradient conductivities.

Typically, the fluidizing gaseous medium is selected to be compatiblewith the tin oxide precursor powder, i.e., to not substantiallyadversely affect the formation of a coating on the substrate duringmelting and ultimate conversion to a tin oxide-containing film.

Generally, gases such as air, nitrogen, argon, helium and the like, canbe used, with air being a gas of choice, where no substantial adverseprehydrolysis or oxidation reaction of the powder precursor takes placeprior to the oxidation-reaction to the tin oxide coating as previouslydiscussed under equilibration and maintaining. The gas flow rate istypically selected to obtain fluidization and charge transfer to thepowder. Fine powders require less gas flow for equivalent deposition. Ithas been found that small amounts of water vapor enhance chargetransfer. The temperature for contacting the substrate with a powderprecursor is generally in the range of about 0° C. to about 100° C. orhigher, more preferably about 20° C. to about 40° C., and still morepreferably about ambient temperature. The substrate however, can be at atemperatures the same as, higher or substantially higher than thepowder.

The time for contacting the substrate with precursor powder is generallya function of the substrate bulk density, thickness, powder size and gasflow rate. The particular coating means is selected in part according tothe above criteria, particularly the geometry of the substrate. Forexample, particles, spheres, flakes, i.e., platelets, short fibers andother similar substrate, can be coated directly in a fluidized bedthemselves with such substrates being in a fluidized motion or state.For fabrics, single fibers, rovings and tows a preferred method is totransport the fabric and/or roving directly through a fluidized bed forpowder contacting. In the case of rovings and tows, a fiber spreader canbe used which exposes the filaments within the fiber bundle to thepowder. The powder coating can be adjusted such that all sides of thesubstrate fabric, roving and the like are contacted with powder. Typicalcontacting time can vary from seconds to minutes, preferably in therange of about 1 second to about 120 seconds, more preferably about 2seconds to about 30 seconds.

Typical tin oxide precursor powders are those that are powders atpowder/substrate contacting conditions and which are liquidous at themaintaining conditions, preferably equilibration conditions, of thepresent process. It is preferred that the powder on meltingsubstantially wets the surface of the substrate, preferably having a lowcontact angle formed by the liquid precursor in contact with thesubstrate and has a relatively low viscosity and low vapor pressure atthe temperature conditions of melting and maintaining, preferablymelting within the range of about 100° C. to about 450° C. or higher,more preferably about 250° C. to about 400° C. Typical powder tin oxideprecursors are stannous chloride, low molecular weight organic salts orcomplexes of tin, particularly low molecular weight organic salts andcomplexes such as stannous acetate and acetylacetonate complexes of tin.

An additional component powder, such as a dopant-forming powder, can becombined with the tin oxide precursor powder. A particularly preferreddopant-forming powder is stannous fluoride. Further, an additionalcomponent, such as a dopant, for example a fluorine or fluoridecomponent, indium, or antimony can be incorporated into the coatingduring the maintaining step, for example hydrogen fluoride gas as asource of fluoride. A combination of the two methods can also be usedfor additional component incorporation.

The powder tin oxide precursor on melting is maintained and/orequilibrated as set forth above. In addition, temperatures can beadjusted and/or a component introduced into the melting/maintaining stepwhich can aid in altering the precursor for enhanced conversion to tinoxide. For example, gaseous hydrogen chloride can be introduced to formpartial or total halide salts and/or the temperature can be adjusted toenhance decomposition of, for example, tin organic salts and/orcomplexes to more readily oxidizable tin compounds. The dopant can alsobe present in an oxide or precursor form in the melt as a dispersedpreferably as a finely dispersed solid. The oxide can be incorporatedadvantageously as part of the powder coating of the substrate material.

A fluidizable coated substrate, such as substrates coated directly in afluid bed of powder, can be subjected to conditions which allowliquidous formation by the tin oxide precursor and coating of thesubstrate. A particularly preferred process uses a film forming amountof the tin oxide precursor which allows for coating during the liquidousstep of the process, and which substantially reduces detrimentalsubstrate agglomeration. The conditions are adjusted or controlled toallow substantially free substrate fluidization and transport under theconditions of temperature and bed density, such as dense bed density tolean bed density. The coated substrate can be further transported to theoxidation step for conversion to tin oxide or converted directly to tinoxide in the same reactor/processing system. A particularly preferredembodiment is the transport of the liquidous coated substrate as a densebed to a fluidized oxidation zone, such zone being a fluidized zonepreferably producing a conversion to tin oxide on the substrate of atleast about 80% by weight.

As set forth above, a particularly unique process and product embodimentof present invention is the preferential coating of the outer poroussubstrate surface while controlling and/or limiting the coating of theinternal pores and surfaces of the porous substrate. The preferredprocess for such selective coating is the coating of a fluidizablecoated substrate with a powder tin oxide precursor. The fluidizationprocess is preferably carried out using a film forming amount of the tinoxide precursor. Such amount allows for coating and distribution on theouter particle surface during the liquidous step of the process. Inaddition, the process allows for control of the oxidation stage of theprocess for converting the tin oxide precursor film to tin oxide. Theprocess parameters and substrate properties can be varied to provide thedesired coating properties for a given application, particularly,surface area in M² /gm, total pore volume (cc/gm) and pore sizedistribution including mean pore diameter, the film forming amount oftin oxide precursor, the temperature of the substrate, melt equilibriumtemperature, residence time during liquidous/equilibrium maintainingoxidation temperature and time. It is preferred to control the residencetime conditions for maintaining to the lower part of the range of about0.05 or 0.1 minute to about 20 minutes, preferably, less than about 0.1minute and still more preferably, less than about 0.05 minutes. Thetemperature of the substrate can be controlled to obtain the desiredcoating properties. For example, a powder coated substrate as set forthabove can be introduced into a fluidization zone which zone is at atemperature above the melt temperature of the tin oxide precursor. Bycontrolling the temperature of the zone and the maintaining residencetime, a temperature differential between the outer surface and internalpores can be obtained which provide for preferential outer surfacecoating. In addition, the tin oxide precursor powder can be added to thefluidization zone in which the substrate is in fluid motion and at atemperature above the melt temperature of the tin oxide precursor. Thetin oxide precursor powder can be introduced into the zone at atemperature below the temperature of the fluidization zone and incontrolled amounts. The powder initially melts preferentially on theouter surface of the substrate. By controlling the maintaining residencetime and by initiating the oxidation step, preferentially when theinitial outer surface coating is achieved, the oxidation of the tinoxide precursor allows for the preferential stabilization and coating ofthe outer surface, i.e., coating of the internal pores of the substrateis reduced, often substantially relative to the coating and distributionthat can occur prior to the oxidation step. It is preferred that thesame reactor processing system be used for both the maintaining andoxidation steps in order to obtain controlled preferential coating ofthe outer surface. As set forth above, various other materials, such as,dopants, catalysts, etc., can be utilized in the process and products ofthis invention.

As set forth above, the properties of the substrates will vary accordingto the application for use of the products. Thus, the physicalproperties, particularly, bulk density, surface area, total pore volume,pore size distribution and apparent porosity can vary and/or beoptimized according to a particular application. The process can bepracticed to preferentially coat the surface of various substrateshaving a range of physical properties and in addition, preferentiallythe outer surface and selective coat, for example, an internal poresurface to a certain depth using the process conditions as set forthabove.

The stannous chloride and/or dopant-forming component to be contactedwith the substrate may be present in a molten state. For example, a meltcontaining molten stannous chloride and/or stannous fluoride and/orother fluoride salt may be used. The molten composition may include oneor more other materials, having properties as noted above, to produce amixture, e.g., a eutectic mixture, having a reduced melting point and/orboiling point. The use of molten stannous chloride and/or dopant-formingcomponent provides advantageous substrate coating while reducing thehandling and disposal problems caused by a solvent. In addition, thesubstrate is very effectively and efficiently coated so that coatingmaterial losses are reduced.

The stannous chloride and/or dopant-forming component to be contactedwith the substrate may be present in a vaporous and/or atomized state.As used in this context, the term "vaporous state" refers to both asubstantially gaseous state and a state in which the stannous chlorideand/or dopant-forming component are present as drops or droplets and/orsolid dispersion such as colloidal dispersion in a carrier gas, i.e., anatomized state. Liquid state stannous chloride and/or dopant-formingcomponent may be utilized to generate such vaporous state compositions.

In addition to the other materials, as noted above, the compositioncontaining stannous chloride and/or the dopant-forming component mayalso include one or more grain growth inhibitor components. Suchinhibitor component or components are present in an amount effective toinhibit grain growth in the tin oxide-containing coating. Reducing graingrowth leads to beneficial coating properties, e.g., higher electricalconductivity, more uniform morphology, and/or greater overall stability.Among useful grain growth inhibitor components are components whichinclude at least one metal, in particular potassium, calcium, magnesium,silicon and mixtures thereof. Of course, such grain growth inhibitorcomponents should have no substantial detrimental effect on the finalproduct.

The dopant-forming component may be deposited on the substrateseparately from the stannous chloride, e.g., before and/or during and/orafter the stannous chloride/substrate contacting. If the dopant-formingcomponent is deposited on the substrate separately from the stannouschloride, it is preferred that the dopant-forming component, forexample, the fluorine component, be deposited after the stannouschloride, such as to form soluble and/or eutectic mixtures and/ordispersions.

Any suitable dopant-forming component may be employed in the presentprocess. Such dopant-forming component should provide sufficient dopantso that the final doped tin oxide coating has the desired properties,e.g., electronic conductivity, stability, etc. Fluorine components areparticularly useful dopant-forming components. Care should be exercisedin choosing the dopant-forming component or components for use. Forexample, the dopant-forming component should be sufficiently compatiblewith the stannous chloride so that the desired doped tin oxide coatingcan be formed. Dopant-forming components which have excessively highboiling points and/or are excessively volatile (relative to stannouschloride), at the conditions employed in the present process, are notpreferred since, for example, the final coating may not be sufficientlydoped and/or a relatively large amount of the dopant-forming componentor components may be lost during processing. It may be useful to includeone or more property altering components, e.g., boiling pointdepressants, in the composition containing the dopant-forming componentto be contacted with the substrate. Such property altering component orcomponents are included in an amount effective to alter one or moreproperties, e.g., boiling point, of the dopant-forming component, e.g.,to improve the compatibility or reduce the incompatibility between thedopant-forming component and stannous chloride.

Particularly useful anion dopants, particularly fluorine components foruse in the present invention are selected from stannous fluoride,stannic fluoride, hydrogen fluoride, ammonium fluoride and mixturesthereof. When stannous fluoride is used as a fluorine component, it ispreferred to use one or more boiling point depressants to reduce theapparent boiling point of the stannous fluoride, in particular to atleast about 850° C. or less. The preferred dopants are those thatprovide for optimum dopant incorporation while minimizing dopantprecursor losses, particularly under the preferred process conditions asset forth therein. In addition oxides or sub-oxides can also be used,including where dopant incorporation is accomplished during theoxidation sintering contacting step.

The use of a fluorine or fluoride dopant is an important feature ofcertain aspects of the present invention. First, it has been found thatfluorine dopants can be effectively and efficiently incorporated intothe tin oxide-containing coating. In addition, such fluorine dopants actto provide tin oxide-containing coatings with good electronic propertiesreferred to above, morphology and stability. This is in contrast tocertain of the prior art which found antimony dopants to be ineffectiveto improve the electronic properties of tin oxide coatings in specificapplications.

The liquid, e.g., molten, composition which includes stannous chloridemay, and preferably does, also include the dopant-forming component. Inthis embodiment, the dopant-forming component or components arepreferably soluble and/or dispersed homogeneously and/or atomized in thecomposition. Vaporous mixtures of stannous chloride and dopant-formingcomponents may also be used. Such compositions are particularlyeffective since the amount of dopant in the final doped tin oxidecoating can be controlled by controlling the make-up of the composition.In addition, both the stannous chloride and dopant-forming component aredeposited on the substrate in one step. Moreover, if stannous fluorideand/or stannic fluoride are used, such fluorine components provide thedopant and are converted to tin oxide during the oxidizingagent/substrate contacting step. This enhances the overall utilizationof the coating components in the present process. Particularly usefulcompositions comprise about 50% to about 98%, more preferably about 70%to about 95%, by weight of stannous chloride and about 2% to about 50%,more preferably about 5% to about 30%, by weight of fluorine component,in particular stannous fluoride.

In one embodiment, a vaporous stannous chloride composition is utilizedto contact the substrate, and the composition is at a higher temperaturethan is the substrate. The make-up of the vaporous stannouschloride-containing composition is such that stannous chloridecondensation occurs on the cooler substrate. If the dopant-formingcomponent is present in the composition, it is preferred that suchdopant-forming component also condense on the substrate. The amount ofcondensation can be controlled by controlling the chemical make-up ofthe vaporous composition and the temperature differential between thecomposition and the substrate. This "condensation" approach veryeffectively coats the substrate to the desired coating thickness withoutrequiring that the substrate be subjected to numerous individual orseparate contactings with the vaporous stannous chloride-containingcomposition. As noted above, previous vapor phase coating methods haveoften been handicapped in requiring that the substrate be repeatedlyrecontacted in order to get the desired coating thickness. The present"condensation" embodiment reduces or eliminates this problem.

The substrate including the stannous chloride-containing coating and thedopant-forming component-containing coating is contacted with anoxidizing agent at conditions effective to convert stannous chloride totin oxide, preferably substantially tin dioxide, and form a doped tinoxide coating on at least a portion of the substrate. Water, e.g., inthe form of a controlled amount of humidity, is preferably presentduring the coated substrate/oxidizing agent contacting. This is incontrast with certain prior tin oxide coating methods which areconducted under anhydrous conditions. The presence of water during thiscontacting has been found to provide a doped tin oxide coating havingexcellent electrical conductivity properties.

Any suitable oxidizing agent may be employed, provided that such agentfunctions as described herein. Preferably, the oxidizing agent (ormixtures of such agents) is substantially gaseous at the coatedsubstrate/oxidizing agent contacting conditions. The oxidizing agentpreferably includes reducible oxygen, i.e., oxygen which is reduced inoxidation state as a result of the coated substrate/oxidizing agentcontacting. More preferably, the oxidizing agent comprises molecularoxygen, either alone or as a component of a gaseous mixture, e.g., air.

The substrate may be composed of any suitable material and may be in anysuitable form. Preferably, the substrate is such so as to minimize orsubstantially eliminate deleterious substrate, coating reactions and/orthe migration of ions and other species, if any, from the substrate tothe tin oxide-containing coating which are deleterious to thefunctioning or performance of the coated substrate in a particularapplication. In addition, it can be precoated to minimize migration, forexample an alumina and/or a silica precoat and/or to improve wetabilityand uniform distribution of the coating materials on the substrate. Inorder to provide for controlled electrical conductivity in the doped tinoxide coating, it is preferred that the substrate be substantiallynon-electronically conductive when the coated substrate is to be used asa component of an electric energy storage battery. In one embodiment,the substrate is inorganic, for example glass and/or ceramic. Althoughthe present process may be employed to coat two dimensional substrates,such as substantially flat surfaces, it has particular applicability incoating three dimensional substrates. Thus, the present process providessubstantial process advances as a three dimensional process. Examples ofthree dimensional substrates which can be coated using the presentprocess include particles, i.e., flakes, extrudates, spheres, singlefibers, chopped fibers, porous substrates, irregularly shaped particles,e.g., catalyst supports and multi-channel monoliths, tubes, conduits,fiber rovings, fiber mats and the like.

The coated porous particles are particularly useful in a number ofapplications, particularly lead acid batteries, for example, monopolarand bipolar batteries, catalysts, resistance heating elements,electrostatic dissipation elements, electromagnetic interferenceshielding elements, electrostatic bleed elements, protective coatings,field dependent fluids and the like. In practice the particles which arepreferred for use in such applications in general have an average lengthin the range of from about 20 microns to about 7 mm and an averagethickness in the range of from about 20 microns to about 7 mm, theaverage length and thickness being different or the same depending onparticle geometry and application. As set forth above, the substratescan be optimized for a particular application and the particularelectrical and/or mechanical requirements associated with such end useapplication. For example, in applications in which the particles arecombined with other materials, such as polymers and positive activematerial of lead acid battery and depending on the requirements of theapplication, ranges of from about 3 microns to about 300 microns, oreven less than about 5 microns, typically ranges of from about 3 micronsto about 150 microns or from about 5 microns to about 75 microns areuseful. For example, processing of a porous coated substrate filledmatrix material, for example a polymer matrix material may be optimizedin substrate porosity for mechanical, structural and reduced weight andby an aspect ratio and/or volume concentration to optimize the formationof for example a conductive network within such matrix material. Theproducts of this invention offer particular advantages in many of suchapplications disclosed herein, including enhanced dispersion andrheology, particularly in various compositions such as polymercompositions, coating compositions, various other liquid and solid typecompositions and systems for producing various products such as coatingsand polymer composites.

As set forth above, the porous inorganic substrates can be characterizedby bulk density (gm/cc) which is the weight or mass per unit volumeconsidered only for the particle itself, i.e., includes the internalpore volume, surface area (M² /gm), total pore volume (cc(hg)/gm), poresize distribution and percent apparent porosity. In general, it ispreferred that the bulk density be from about 3% to about 85% morepreferably from about 10% to about 70%, more preferably, from about 10%to about 60% of the true density of the substrate material. Bulkdensities less than about 5% are also useful. In addition, the poroussubstrate can have a wide range of surface area (M² /gm) of from about0.01 to about 700 preferably having a moderate to high surface area,preferably, from about 10M² /gm to about 600M² /gm, more preferably,from about 50M² /gm to about 500M² /gm. The pore volume is preferablyfrom about 0.4 cc/gm to about 3.5 cc/gm, or even up to about 5 cc/gm,more preferably from about 0.7 cc/gm to about 3.50 cc/gm or even up toabout 4.5 cc/gm more preferably from about 0.7 cc/gm to about 3.25cc/gm. The pore size distribution can vary over a wide range and canhave various distributions including multi-modal, for example, bi-modaldistribution of pores including macro pores and micro pores. Thereideally exists a relationship between pore diameter, surface area andpore volume, thus fixing any two variables generally determines thethird. In general, the mean (50%) pore diameter for macro pores, i.e.,generally classified as having a pore diameter greater than about 750angstroms can vary from about 0.075 microns to about 150 microns, morepreferably, from about 0.075 microns to about 10 microns. Microporosity, generally classified as a porosity having a mean pore diameterof less than about 750 angstroms can vary over a wide range. In general,the mean pore diameter for micro porosity can vary from about 20angstroms to about 750 angstroms, more preferably, from about 70angstroms to about 600 angstroms. The ratio of macro to micro porositycan vary over a wide range and depending on the application, can bevaried to provide optimized performance as more fully set forth underthe various applications. In general, the ratio of percent macroporosity to micro porosity expressed as that percent of the totalporosity can vary from about 0% to about 95%, more preferably, fromabout 5% to about 80% macro porosity and from about 100% to about 5%,more preferably from about 95% to about 20% micro porosity.

As set forth above, the porous substrate can be inorganic for example,carbon and carbide, i.e., silicon carbide and/or an inorganic oxide.Typical examples of inorganic oxides which are useful as substratesinclude for example, substrates containing one or more alumino silicate,silica, alumina, zirconia, magnesia, boria, phosphate, titania, ceria,thoria and the like, as well as multi-oxide type supports such asalumina-phosphorous oxide, silica alumina, zeolite modified inorganicoxides, e.g., silica alumina, perovskites, spinels, aluminates,silicates, e.g., zirconium silicate, mixtures thereof and the like. Asset forth above, porous substrate materials can be in many forms andshapes, especially shapes which are not flat surfaces, i.e., nonline-of-site materials such as pellets, extrudates, beads,includingspheres, flakes, aggregates, rings, saddles, stars and the like. Thepercent apparent porosity, i.e., the volume of open pores expressed as apercentage of the external volume can vary over a wide range and ingeneral, can vary from about 20% to about 92%, more preferably, fromabout 40% to about 90%. In practice, the bead particles, includingspheres, which are preferred for use in such applications in generalhave a roundness associated with such particles generally greater thanabout 70% still more preferably, greater than about 85% an still morepreferably, greater than about 95%. The bead products of this inventionoffer particular advantages in many of such applications disclosedherein, including enhanced dispersion and rheology, particularly, invarious compositions such as polymer compositions, coating compositions,various other liquid and solid type compositions and systems forproducing various products such as coatings and polymer composites.

The particular substrate, including chemical composition can beoptimized for the processing conditions utilized to coat the substratewith tin oxide. In general, the substrate and process conditions areselected to provide preferential outer surface coating, includingcapillary effects reduce adverse substrate tin oxide precursorinteractions and/or substrate decomposition which is substantiallydeleterious to the final properties of the tin oxide coated substrate.The preferred inorganic oxides for various applications, as well as theaverage particle size, density and additional components associated withthe tin dioxide coated porous particle, are set forth below under leadacid batteries, catalysts, resistance heating elements, electrostaticdissipation elements, electromagnetic interference shielding elements,electrostatic bleed elements, protective coatings, field dependentfluids and the like.

Acid resistant inorganic substrates, especially fibers, flakes, andwoven and non-woven mats of acid resistant glass fibers, areparticularly useful substrates when the doped tin oxide coated substrateis to be used as a component of a battery, such as a lead-acidelectrical energy storage battery. More particularly, the substrate foruse in a battery, particularly a bipolar battery is in or can be in theform of a body of woven or non-woven fibers, still more particularly, abody of fibers having a porosity in the range of about 60% to about 95%.Porosity is defined as the percent or fraction of void space within abody of fibers. The above-noted porosities are calculated based on thefibers including the desired fluorine doped tin oxide coating.

The porous substrate for use in lead-acid batteries, because ofavailability, cost and performance considerations, generally comprisesacid resistant glass, and/or ceramics more preferably in the form ofparticles, for example, fibers, and/or flakes, and/or beads includingspheres and/or extrudates as noted above.

The substrate for use in lead-acid batteries is acid resistant. That is,the substrate exhibits some resistance to corrosion, erosion and/orother forms of deterioration at the conditions present, e.g., at or nearthe positive plate, or positive side of the bipolar plates, in alead-acid battery. Although the fluorine doped tin oxide coating doesprovide a degree of protection for the substrate against theseconditions, the substrate should itself have an inherent degree of acidresistance. If the substrate is acid resistant, the physical integrityand electrical effectiveness of the doped tin oxide coating and of thewhole present battery element, is better maintained with time relativeto a substrate having reduced acid resistance. If glass is used as thesubstrate, it is preferred that the glass have an increased acidresistance relative to E-glass. Preferably, the acid resistant glasssubstrate is at least as resistant as is C-or T- glass to the conditionspresent in a lead-acid battery.

Typical compositions of E-glass and C-glass are as follows:

    ______________________________________                                                     Weight Percent                                                                E-glass C-glass   T-glass                                        ______________________________________                                        Silica         54        65        65                                         Alumina        14         4         6                                         Calcia         18        14        10*                                        Magnesia        5         3        --                                         Soda +          0.5       9        13                                         Potassium Oxide                                                               Boria           8         5         6                                         Titania +       0.5      --        --                                         Iron Oxide                                                                    ______________________________________                                         *including MgO                                                           

Preferably the glass contains more than about 60% by weight of silicaand less than about 35% by weight of alumina, and alkali and alkalineearth metal oxides.

As set forth above, one of the preferred applications for use of thecoated porous substrates is in lead acid batteries. Thus, the coatedsubstrates can be added directly to the positive active material of alead acid battery, i.e., the positive electrode to improve batteryperformance, particularly, positive active material utilizationefficiency, formation efficiency and recharge efficiency. Oneparticular, unique aspect of the coated porous substrates is that thecoated substrate has both enhanced properties from the conductivecoating and in addition, is able to provide an internal reservoir forholding sulfuric acid electrolyte required for carrying out theelectro-chemical reactions in the positive active material. Moreparticularly, the combination of conductive coating and porosityimproves overall, high rate performance of the positive active material,i.e., improved utilization efficiency at varying rates of dischargetime, including high rates and at short discharge times.

As set forth above, the physical properties of the porous substrates canvary widely. It is preferred that the substrate have sufficient macroporosity and percent apparent porosity to allow for the utilization ofthe electrolyte sulfuric acid contained in the pores during discharge ofthe positive active material and, in addition, that the bulk density beselected to reduce the overall weight of the positive active materialwhile enhancing the overall performance of the battery. In general, thepreferable percent apparent porosity can vary from about 40% to about92%, more preferably, from about 70% to about 90%. The preferred ratioof percent macro porosity to percent micro porosity can vary over a widerange and in general is from about 20% to about 95% macro porosity, morepreferably, from about 45% to about 90% macro porosity with the balancebeing micro porosity. The mean pore diameter, particularly mean macropore diameter, can vary over a wide range with the utilization ofelectrolyte during the condition of the discharge of the battery beingan important factor i.e., at high rate discharges, such as coldcranking, high macro porosity is preferred. Preferred mean macro porediameter is from about 1 micron to about 150 microns, more preferably,from about 5 to about 100 microns or even from about 0.075 micron toabout 10 micron and still more preferably from about 0.1 to about 5microns.

As set forth above, a particularly preferred substrate is a porousparticle, i.e. porous support, particularly beads, including spheres,extrudates, pellets, rings, saddles, stars, etc., preferably within thebulk density, macro porosity, micro porosity, apparent percent porosityand surface areas as set forth above. The coated particles can provideimproved performance in various applications, particularly, in thepositive active material of lead acid batteries. As set forth above, theporous substrate can provide a reservoir for electrolyte sulfuric acidwhich participates in the electrochemical reaction during discharge ofthe positive active material. A particularly unique embodiment of thepresent invention is the use of the porous substrate itself as anadditive in the positive active material to provide a reservoir ofelectrolyte sulfuric acid while providing a light weight additive forincorporation into the positive active material. Such particles areporous and within the ranges as set forth above for the coated poroussubstrates, particularly the preferred ranges. Such porous substratescan be further coated with additional components such as with othersurface components, which may improve recharge, i.e. oxidation as wellas other conductive components. As set forth above, the porous substratewith or without an additional component provides unexpected improvementin the performance of the positive active material, particularly, in thehigh rate discharge conditions such as cold cranking under lower thanambient temperature conditions.

As set forth above the porous substrate are acid resistant and include awide variety of materials, including inorganic and organic basedmaterials. The porous substrates can be in a wide variety of shapes,including shapes that are reduced in size during the manufacture of thepositive active material, such as in the blending and/or mixing of theporous substrate in positive active material manufacture. It ispreferred that the resulting particles if reduced in size maintainporosity parameters within the ranges as set forth above. It is alsopreferred, that the particles have sufficient stiffness and orresistance to detrimental permanent deformation in order to maintainsufficient porosity for the sulfuric acid in the pores to participate ina number of repetitive discharge and charge cycles, such as greater than50 cycles or even 100 cycles.

The conditions at which each of the steps of the present process occurare effective to obtain the desired result from each such step and toprovide a substrate coated with a tin oxide-containing coating. Thesubstrate/stannous chloride contacting and the substrate/dopant-formingcomponent contacting preferably occur at a temperature in the range ofabout 250° C. to about 375° C., more preferably about 275° C. to about350° C. The amount of time during which stannous chloride and/ordopant-forming component is being deposited on the substrate depends ona number of factors, for example, the desired thickness of the tinoxide-containing coating, the amounts of stannous chloride anddopant-forming component available for substrate contacting, the methodby which the stannous chloride and dopant-forming component arecontacted with the substrate and the like. Such amount of time ispreferably in the range of about 0.5 minutes to about 20 minutes, morepreferably about 1 minute to about 10 minutes.

If the coated substrate is maintained in a substantially non-deleteriousoxidizing environment, as previously set forth, it is preferred thatsuch maintaining occur at a temperature in the range of about 275° C. toabout 375° C., more preferably about 300° C. to about 350° C. for aperiod of time in the range of about 0.1 minutes to about 20 minutes,more preferably about 1 minute to about 10 minutes. The coatedsubstrate/oxidizing agent contacting preferably occurs at a temperaturein the range of about 350° C. to about 600° C., more preferably about400° C. to about 550° C., for a period of time in the range of about 0.1minutes to about 10 minutes. A particular advantage of the process ofthis invention is the temperatures used for oxidation have been found tobe lower, in certain cases, significantly lower, i.e., 50° to 100° C.than the temperatures required for spray hydrolysis. This is verysignificant and unexpected, provides for process efficiencies andreduces, and in some cases substan-tially eliminates, deleteriousreactions and/or migration of deleterious elements from the substrate tothe tin oxide layer. Excessive sodium migration, e.g., from thesubstrate, can reduce electronic conductivity.

The pressure existing or maintained during each of these steps may beindependently selected from elevated pressures (relative to atmosphericpressure), atmospheric pressure, and reduced pressures (relative toatmospheric pressure). Slightly reduced pressures, e.g., less thanatmospheric pressure and greater than about 8 psia and especiallygreater than about 11 psia, are preferred.

The tin oxide coated substrate, such as the fluorine doped tin oxidecoated substrate, of the present invention may be, for example, acatalyst itself or a component of a product, such as a compositetogether with one or more matrix materials. The composites may be suchthat the matrix material or materials substantially totally encapsulateor surround the coated substrate, or a portion of the coated substratemay extend away from the matrix material or materials.

Any suitable matrix material or materials may be used in a compositewith the tin oxide coated substrate. Preferably, the matrix materialcomprises a polymeric material, e.g., one or more synthetic polymers,more preferably an organic polymeric material. The polymeric materialmay be either a thermoplastic material or a thermoset material. Amongthe thermoplastics useful in the present invention are the polyolefins,such as polyethylene, polypropylene, polymethylpentene and mixturesthereof; and poly vinyl polymers, such as polystyrene, polyvinylidenedifluoride, combinations of polyphenylene oxide and polystyrene, andmixtures thereof. Among the thermoset polymers useful in the presentinvention are epoxies, phenol-formaldehyde polymers, polyesters,polyvinyl esters, polyurethanes, melamine-formaldehyde polymers, andurea-formaldehyde polymers.

Further, the porous substrate as set forth above can be an acidresistant organic material, including organic polymeric materials as setforth above. Preferred polymers are polyolefin polymers, polyvinylpolymers, phenolformaldehyde polymers, polyesters, polyvinylesters andmixtures thereof. Preferred polymers are polyolefins, preferablypolypropylene, phenolformaldehyde polymers and polyvinylester,particularly modacrylic polymers.

When used in battery applications, the present doped tin oxide coatedsubstrate is preferably at least partially embedded in a matrixmaterial. The matrix material should be at least initially fluidimpervious to be useful in bipolar batteries. If the fluorine doped tinoxide coated substrate is to be used as a component in a battery, e.g.,a lead-acid electrical energy storage battery, it is situated so that atleast a portion of it contacts the positive active electrode material.Any suitable positive active electrode material or combination ofmaterials useful in lead-acid batteries may be employed in the presentinvention. One particularly useful positive active electrode materialcomprises electrochemically active lead oxide, e.g., lead dioxide,material. A paste of this material is often used. If a paste is used inthe present invention, it is applied so that there is appropriatecontacting between the fluorine doped tin oxide coated substrate and thepaste.

In order to provide enhanced bonding between the tin oxide coatedsubstrate and the matrix material, such as a polymer matrix, it has beenfound that the preferred matrix materials have an increased polarity, asindicated by an increased dipole moment, relative to the polarity ofpolypropylene. Because of weight and strength considerations, if thematrix material is to be a thermoplastic polymer, it is preferred thatthe matrix be a polypropylene-based polymer which includes one or moregroups effective to increase the polarity of the polymer relative topolypropylene. Additive or additional monomers, such as maleicanhydride, vinyl acetate, acrylic acid, and the like and mixturesthereof, may be included prior to propylene polymerization to give theproduct propylene-based polymer increased polarity. Hydroxyl groups mayalso be included in a limited amount, using conventional techniques, toincrease the polarity of the final propylene-based polymer.

Thermoset polymers which have increased polarity relative topolypropylene are more preferred for use as the present matrix material.Particularly preferred thermoset polymers include epoxies,phenol-formaldehyde polymers, polyesters, and polyvinyl esters.

A more complete discussion of the presently useful matrix materials ispresented in Fitzgerald, et al U.S. Pat. No. 4,708,918, the entiredisclosure of which is hereby incorporated by reference herein.

Various techniques, such as casting, molding and the like, may be usedto at least partially encapsulate or embed the tin oxide coatedsubstrate into the matrix material or materials and form composites. Thechoice of technique may depend, for example, on the type of matrixmaterial used, the type and form of the substrate used and the specificapplication involved. Certain of these techniques are presented in U.S.Pat. No. 4,547,443, the entire disclosure of which is herebyincorporated by reference herein. One particular embodiment involvespre-impregnating (or combining) that portion of the tin oxide coatedsubstrate to be embedded in the matrix material with a relatively polar(increased polarity relative to polypropylene) thermoplastic polymer,such as polyvinylidene difluoride, prior to the coated substrate beingembedded in the matrix material. This embodiment is particularly usefulwhen the matrix material is itself a thermoplastic polymer, such asmodified polypropylene, and has been found to provide improved bondingbetween the tin oxide coated substrate and the matrix material.

The bonding between the matrix material and the fluorine doped tin oxidecoated, acid-resistant substrate is important to provide effectivebattery operation. In order to provide for improved bonding of thefluorine doped tin oxide coating (on the substrate) with the matrixmaterial, it is preferred to at least partially, more preferablysubstantially totally, coat the fluorine doped tin oxide coatedsubstrate with a coupling agent which acts to improve the bonding of thefluorine doped tin oxide coating with the matrix. This is particularlyuseful when the substrate comprises acid resistant glass fibers. Anysuitable coupling agent may be employed. Such agents preferably comprisemolecules which have both a polar portion and a non-polar portion.Certain materials generally in use as sizing for glass fibers may beused here as a "size" for the doped tin oxide coated glass fibers. Theamount of coupling agent used to coat the fluorine doped tin oxidecoated glass fibers should be effective to provide the improved bondingnoted above and, preferably, is substantially the same as is used tosize bare glass fibers. Preferably, the coupling agent is selected fromthe group consisting of silanes, silane derivatives, stannates, stannatederivatives, titanates, titanate derivatives and mixtures thereof. U.S.Pat. No. 4,154,638 discloses one silane-based coupling agent adapted foruse with tin oxide surfaces. The entire disclosure of this patent ishereby expressly incorporated by reference herein.

In the embodiment in which the fluorine doped tin oxide coated substrateis used as a component of a bipolar plate in a lead-acid battery, it ispreferred to include a fluid-impervious conductive layer that isresistant to reduction adjacent to, and preferably in electricalcommunication with, the second surface of the matrix material. Theconductive layer is preferably selected from metal, more preferablylead, and substantially non-conductive polymers, more preferablysynthetic polymers, containing conductive material. The non-conductivepolymers may be chosen from the polymers discussed previously as matrixmaterials. One particular embodiment involves using the same polymer inthe matrix material and in the conductive layer. The electricallyconductive material contained in the non-conductive layer preferably isselected from the group consisting of graphite, lead and mixturesthereof.

In the bipolar plate configuration, a negative active electrode layerlocated to, and preferably in electric communication with, the fluidimpervious conductive layer is included. Any suitable negative activeelectrode material useful in lead-acid batteries may be employed. Oneparticularly useful negative active electrode material comprises lead,e.g., sponge lead. Lead paste is often used.

In yet another embodiment, a coated substrate including tin oxide,preferably electronically conductive tin oxide, and at least oneadditional catalyst component in an amount effective to promote achemical reaction is formed. Preferably, the additional catalystcomponent is a metal and/or a component of a metal effective to promotethe chemical reaction. The promoting effect of the catalyst componentmay be enhanced by the presence of an electrical field or electricalcurrent in proximity to the component. Thus, the tin oxide, preferablyon a substantially non-electronically conductive substrate, e.g., acatalyst support, can provide an effective and efficient catalyst forchemical reactions, including those which occur or are enhanced when anelectric field or current is applied in proximity to the catalystcomponent. Thus, it has been found that the present coated substratesare useful as active catalysts and supports for additional catalyticcomponents. Without wishing to limit the invention to any particulartheory of operation, it is believed that the outstanding stability,e.g., with respect to electronic properties and/or morphology and/orstability, of the present tin oxides plays an important role in makinguseful and effective catalyst materials, particularly the higher surfacearea attainable tin oxide materials prepared in accordance with thisinvention, especially when compared to prior art processes which producevery low surface areas. Any chemical reaction, including a chemicalreaction the rate of which is enhanced by the presence of an electricalfield or electrical current as described herein, may be promoted usingthe present catalyst component tin oxide-containing coated substrates. Aparticularly useful class of chemical reactions are those involvingchemical oxidation or reduction. For example, an especially useful andnovel chemical reduction includes the chemical reduction of nitrogenoxides, to minimize air pollution, with a reducing gas such as carbonmonoxide, hydrogen and mixtures thereof and/or an electron transferringelectrical field. A particularly useful chemical oxidation applicationis a combustion, particularly catalytic combustion, wherein theoxidizable compounds, i.e., carbon monoxide and hydrocarbons arecombusted to carbon dioxide and water. For example, catalytic convertersare used for the control of exhaust gases from internal combustionengines and are used to reduce carbon monoxide and hydrocarbons fromsuch engines. Of course, other chemical reactions, e.g., hydrocarbonreforming, dehydrogenation, such as alkylaromatics to olefins andolefins to dienes, hydrodecyclization, isomerization, ammoxidation, suchas with olefins, aldol condensations using aldehydes and carboxylicacids and the like, may be promoted using the present catalystcomponent, tin oxide-containing coated substrates. As noted above, it ispreferred that the tin oxide in the catalyst component, tinoxide-containing substrates be electronically conductive. Althoughfluorine doped tin oxide is particularly useful, other dopants may beincorporated in the present catalyst materials to provide the tin oxidewith the desired electronic properties. For example, antimony may beemployed as a tin oxide dopant. Such other dopants may be incorporatedinto the final catalyst component, tin oxide-containing coatedsubstrates using one or more processing techniques substantiallyanalogous to procedures useful to incorporate fluorine dopant, e.g., asdescribed herein.

Particularly useful chemical reactions as set forth above include theoxidative dehydrogenation of ethylbenzene to styrene and 1-butene to1,3-butadiene; the ammoxidation of propylene to acrylonitrile; aldolcondensation reactions for the production of unsaturated acids, i.e.,formaldehyde and propionic acid to form methacrylic acid andformaldehyde and acetic acid to form acrylic acid; the isomerization ofbutenes; and the oxidation of methane to methanol. It is believed,without limiting the invention to any specific theory of operation, thatthe stability of the catalysts, the redox activity of the tin oxide,i.e., stannous, stannic, mixed tin oxide redox couple, morphology andthe tin oxide catalytic and/or support interaction with other catalyticspecies provides for the making of useful and effective catalystmaterials. In certain catalytic reactions, such as NO_(x) reduction andoxidative dehydrogenation, it is believed that lattice oxygen from theregenerable tin oxide redox couple participates in the reactions.

The tin oxide-containing coated substrates of the present invention maybe employed alone or as a catalyst and/or support in a sensor, inparticular gas sensors. Preferably, the coated substrates includes asensing component similar to the catalyst component, as describedherein. The present sensors are useful to sense the presence orconcentration of a component, e.g., a gaseous component, of interest ina medium, for example, hydrogen, carbon monoxide, methane and otheralkanes, alcohols, aromatics, e.g., benzene, water, etc., e.g., byproviding a signal in response to the presence or concentration of acomponent of interest, e.g., a gas of interest, in a medium. Suchsensors are also useful where the signal provided is enhanced by thepresence of an electrical field or current in proximity to the sensingcomponent. The sensing component is preferably one or more metals ormetallic containing sensing components, for example, platinum,palladium, silver and zinc. The signal provided may be the result of thecomponent of interest itself impacting the sensing component and/or itmay be the result of the component of interest being chemically reacted,e.g., oxidized or reduced, in the presence of the sensing component.

The stability and durability for the present tin oxide materials arebelieved to make them very useful as catalysts, sensors, and supportsfor additional catalysts and sensors in aggressive and/or harshenvironments, particularly acid, i.e., sulfur and nitrogen acidenvironments.

Any suitable catalyst component (or sensing component) may be employed,provided that it functions as described herein. Among the useful metalcatalytic components and metal sensing components are those selectedfrom components of the transition metals, the rare earth metals, certainother catalytic components and mixtures thereof, in particular catalystscontaining gold, silver, copper, vanadium, chromium, cobalt molybdenum,tungsten, zinc, indium, the platinum group metals, i.e., platinum,palladium and rhodium, iron, nickel, manganese, cesium, titanium, etc.Although metal containing compounds may be employed, it is preferredthat the metal catalyst component (and/or metal sensing component)included with the coated substrate comprise elemental metal and/or metalin one or more active oxidized forms, for example, Cr₂ O₃, Ag₂ O, etc.

As set forth above, the preferred support materials include a widevariety of materials used to support catalytic species, particularlyporous refractory inorganic oxides. These supports include, for example,alumina, silica, zirconia, magnesia, boria, phosphate, titania, ceria,thoria and the like, as well as multi-oxide type supports such asalumina-phosphorous oxide, silica alumina, zeolite modified inorganicoxides, e.g., silica alumina, and the like. As set forth above, supportmaterials can be in many forms and shapes, especially porous shapeswhich are not flat surfaces, i.e., non line-of-site materials.Particularly useful catalyst supports are for example, porous particles,such as beads extrudates, pellets and other shapes as set forth aboveand a multi-channel monolith such as one made from cordierite which hasbeen coated with alumina. The catalyst materials can be used as is orfurther processed such as by sintering of powered catalyst materialsinto larger aggregates. The aggregates can incorporate other powders,for example, other oxides, to form the aggregates.

As set forth above, the inorganic substrates, can include a wide varietyof materials. Further examples of inorganic oxides for use in themanufacture of porous particles and monoliths are for example,cordierite, silicon carbide, silicon nitride, titania (such as anatase),alumina (preferably gamma alumina), titania and silica, magnesiumaluminate spinel, mordenite, i.e., zeolite, silica, magnesia andmixtures thereof. The inorganic substrates, particularly the inorganicoxide supports are particularly useful and can be coated with a tinoxide forming component and converted to a tin oxide. The catalystcomponents (or sensing components) may be included with the coatedsubstrate using any one or more of various techniques, e.g.,conventional and well known techniques. For example, metal catalystcomponents (metal sensing components) can be included with the coatedsubstrate by impregnation; electro-chemical deposition; sprayhydrolysis; deposition from a molten salt mixture; thermal decompositionof a metal compound or the like. The amount of catalyst component (orsensing component) included is sufficient to perform the desiredcatalytic (or sensing function), respectively, and varies fromapplication to application. In one embodiment, the catalyst component(or sensing component) is incorporated while the tin oxide formingcomponent is placed on the substrate. Thus, a catalyst material, such asa salt or acid, e.g., a halide and preferably chloride, oxy chloride andchloro acids, e.g., chloro platinic acid, of the catalytic metal, isincorporated into the stannous chloride-containing coating of thesubstrate, prior to contact with the oxidizing agent, as describedherein. This catalyst material can be combined with the stannouschloride and contacted with the substrate, or it may be contacted withthe substrate separately from stannous chloride before, during and/orafter the stannous chloride/substrate contacting.

One approach is to incorporate catalyst-forming materials into a processstep used to form a tin oxide coating. This minimizes the number ofprocess steps but also, in certain cases, produces more effectivecatalysts. The choice of approach, however, is dependent on a number offactors, including the process compatibility of tin oxide andcatalyst-forming materials under given process conditions and theoverall process efficiency and catalyst effectiveness.

The catalyst support and/or tin oxide coated support can be coated witha material, such as a high surface area forming material, for example awash coat in order to increase surface area. It is preferred to form ahigh surface area prior to incorporating the active catalyst material.Various conventional and well known techniques for catalystincorporation can be used.

As is known in the art, certain particulate supports can be madedirectly with high surface areas, however, others, can have low surfaceareas, i.e., about 0.1 to about 2 meter square per gram. Such surfaceareas are less than optimized for catalytic activity. In order toincrease surface area, particularly for monoliths, the support can becoated with a high surface area material, such as an oxide formingmaterial, particularly gamma alumina.

The thickness of the wash coat is generally less than about 0.1 mm. Moretypically, less than about 0.05 mm on the basis of overall averagethickness. The coating generally comprises macro pores in the range ofabout 2 to about 10 microns and meso pores of from about 100 to about200 angstroms. The type of distribution of pore size is generallyreferred to as a bimodal pore distribution.

As set forth above, the catalyst support can be coated with materials toprovide and/or enhance a particular property. In addition to surfacearea, coatings can also incorporate an active catalyst component. Forexample, zeolites can be coated on the surface of the catalyst support,using for example a silica binder generally in the range from about 10to 40 wt % binder, more preferably from about 20 to about 30 wt %binder. The concentration of binder is selected to maximize theavailability of zeolite sites and to preserve the integrity of thecoating.

A wide variety of materials, for example, inorganic oxides, can be usedin the manufacture of catalysts. As set forth above, it is preferred toreduce deleterious interactions between the substrate and the tin oxidecoating on the substrate, i.e., a deleterious interaction whichsubstantially reduces the conductivity and/or catalyst activity and/oractivity maintenance for the particular application. In addition, it ispreferred to reduce deleterious interactions between non-tin oxidecoatings with the active catalyst component where such additionalcoatings are utilized in the preparation of the catalyst.

As set forth above, the catalyst can be contacted with a tin oxideprecursor, utilizing for example powder, slurry, vapor infiltration andthe like, process to produce a coated substrate. In a preferredembodiment, the tin oxide precursor is converted to tin oxide followedby incorporation of the catalyst component. The catalyst component canbe incorporated directly on the tin oxide surface and/or a coating suchas a high surface area coating, can be applied to the tin oxide surfacecoating, prior to incorporation of the active catalyst component. Ingeneral, it is preferred to have a high surface area available forcatalyst incorporation and dispersion, particularly for high activitycatalysts used in high gas velocity type conversion processes. Theselection of a coating such as a coating on the tin oxide surface, is inpart a function of the chemical process, the chemical processingconditions, to which the catalyst surface is exposed. For example,deleterious reactions between the catalyst and/or coating, i.e., theformation of low temperature spinels, from the catalyst component andfor example alumina component can reduce significantly both catalystactivity and activity maintenance. Such coatings are selected to reducesuch deleterious interactions between the catalyst and coating and/ortin oxide surface. However, certain catalyst coating interactions,enhance catalyst activity conversion and activity maintenance. Suchinteractions are generally referred to as catalyst support interactionsand/or strong catalyst support interactions. Catalyst components,coatings, including tin oxide coating, can be selected to enhance suchcatalyst support interactions.

As set forth above, the support can be coated with a barrier typecoating, prior to contacting with a tin oxide precursor and subsequentconversion to a tin oxide coating on the monolith. The barrier coat canreduce substantial deleterious substrate/tin oxide interaction, as wellas, providing a definable surface, generally from a porosity standpoint, to control and/or regulate the quantity of tin oxide precursorused to obtain a design average coating thickness, including reducedpenetration into the pores of the catalyst. In addition, a coating canbe formed on the tin oxide surface to provide for improved catalystperformance, i.e., higher surface area, more effective dispersion ofcatalyst, interactions between the coating and catalyst which improvescatalysts performance, i.e., catalyst coating interactions which improvecatalyst performance and/or reduce deleterious interactions whichsubstantially reduce overall catalyst performance. As set forth above,the tin oxide and added catalyst metal can be formed with or without theuse of a coating on the tin oxide surface, with the use of a subsequentcoating, i.e, a high surface area coating being a preferred approach toincorporate catalyst forming materials. The tin oxide coating, catalystcombinations, as set forth above, are preferred catalyst products of thepresent invention.

As set forth above, one of the preferred applications for the use ofcoated porous substrates is in catalysis. Thus, coated substrates havinga controlled amount of coating on the outer surfaces while limiting thecoating on the internal surfaces, allows a catalysis component to beincorporated on the coated surface and the uncoated surface, thusallowing for improved catalyst performance. For example, oneparticularly unique aspect of the coated porous substrate is that thecoating on the substrate can have an enhanced property from theconductive coating and in addition, the substrate can provide aninternal pore volume and surface area for incorporation of a catalyticmaterial for carrying out catalytic reactions. Thus, for example, thecoating can provide a surface which can be catalytic have improvedabrasion resistance and in addition, resistively heated to allow thesurface temperature to increase to reaction conditions by theapplication of, for example, a potential across a fixed bed ofconductive particles having surface to surface contact for maintainingan electrical circuit. These feature can be particularly advantageouswhere the initiation of the chemical reaction is very important, such asthe combustion of carbon monoxide and hydrocarbon during the earlyminutes of operation of an internal combustion engine or in particulatetraps for example in the burning off of soot carbon. In addition, thecoating of the outer surface for purposes of electroconductivity canallow for a reduction in eight of the particle based upon the uncoated,internal pore volume that remains in the particle.

As set forth above, the physical properties of the porous substrates canvary widely. It is preferred that the substrate have sufficient microporosity and surface area to allow for improved catalytic activity ofthe catalyst contained on the surface and in the pores of the substrate.In general, the preferred range of mean micro pore diameter is fromabout 20 angstroms to about 600 angstroms, more preferably, from about40 angstroms to about 150 angstroms. In general, the preferred meanmacro pore diameter is from about 0.075 microns to about 10 microns,more preferably, from about 0.075 microns to about 5 microns. Thepreferred ratio of percent macro porosity to percent micro porosity canvary over a wide range and in general is from about 0% to about 40%macro porosity, more preferably, from about 5% to about 25% macroporosity with the balance being micro porosity.

As set forth above, the tin oxide substrate can be contacted with thecatalyst forming material to incorporate the catalyst material after theconversion of the tin oxide precursor to tin oxide. As set forth above,various techniques, e.g., conventional and well known techniques can beutilized, i.e., impregnation and deposition from salt mixtures. Forexample, the tungsten and molybdenum can be incorporated as a catalystby impregnation using ammonium salts dissolved in base. In addition,vanadium, i,e., ammonium vanadate dissolved in for example, a polyfunctional acid such as oxalic acid can be used. Metals such as cobalt,nickel, iron and copper can be impregnated as a nitrate solution. Theimpregnated supports are typically dried and sintered at elevatedtemperature for a time sufficient to decompose the salt to thecorresponding oxide. Conventional and well known techniques can beutilized for metals such as the incorporation of precious metals ascatalyst. As set forth above, a preferred impregnation technique forprecious metal particularly, platinum is the use of chloro platinicacid. Aqueous and/or non-aqueous systems can be used with the mediumbeing preferred which reduces and/or minimizes substantiallydeleter-ious effects on the support such as in pore size and/or surfacearea and/or pore size distribution. The impregnation or other techniquesto incorporate a catalyst material after the formation of the tin oxidecoating, is particularly preferred when the substrate is a multi-channelmonolith.

The tin oxide/substrate combinations, e.g., the tin oxide coatedsubstrates, of the present invention are useful in other applications aswell. Among these other applications are included porous membranes,resistance heating elements, electrostatic dissipation elements,electromagnetic interference shielding elements, protective coatings,field dependent fluids and the like.

In one embodiment, a porous membrane is provided which comprises aporous substrate, preferably an inorganic substrate, and a tinoxide-containing material in contact with at least a portion of theporous substrate. In another embodiment, the porous membrane comprises aporous organic matrix material, e.g., a porous polymeric matrixmaterial, and a tin oxide-containing material in contact with at least aportion of the porous organic matrix material. With the organic matrixmaterial, the tin oxide-containing material may be present in the formof an inorganic substrate, porous or substantially non porous, having atin oxide-containing coating, e.g., an electronically conductive tinoxide-containing coating, thereon.

One particularly useful feature of the present porous membranes is theability to control the amount of tin oxide present to provide forenhanced performance in a specific application, e.g., a specificcontacting process. For example, the thickness of the tinoxide-containing coating can be controlled to provide such enhancedperformance. The coating process of the present invention isparticularly advantageous in providing such controlled coatingthickness. Also, the thickness of the tin oxide-containing coating canbe varied, e.g., over different areas of the same porous membrane, suchas an asymmetric porous membrane. In fact, the thickness of this coatingcan effect the size, e.g., diameter, of the pores. The size of the poresof the membrane or porous substrate may vary inversely with thethickness of the coating. The coating process of the present inventionis particularly useful in providing this porosity control.

As set forth above, one of the preferred applications for use of thecoated porous substrates is as porous membranes. Thus, the coatedsubstrates can be controlled in the amount of tin oxide present on theouter surface versus internal surfaces to provide enhanced performance.This control is particularly useful when the porous membrane is to beused in combination with an applied force field enhance separation invarious separation processes.

A heating element, for example, a resistance heating element, isprovided which comprises a three dimensional substrate including aporous inorganic substrate having an electrically or electronicallyconductive tin oxide-containing coating on at least a portion of allthree dimensions thereof. The coated substrate is adapted and structuredto provide heat in response, that is, in direct or indirect response, tothe presence or application of one or more force fields, for example,magnetic fields, electrical fields or potentials, combinations of suchforce fields and the like, therein or thereto. An example of such aheating element is one which is adapted and structured to provide heatupon the application of an electrical potential across the coatedsubstrate. Heating elements which are adapted and structured to provideheat in response to the presence of one or more electrical currentsand/or electrical fields and/or magnetic fields therein are included inthe scope of the present invention. The heat may be generatedresistively. As set forth above, one of the preferred coated substratesis a porous coated substrate wherein the outer surface is coated whilethe coating is limited in the internal surfaces. This feature isparticularly useful in resistance heating applications wherein outersurface to outer surface contact between particles is used to produceheat in direct response to a field or potential. In addition, the outercoating can generate heat on the outer surface in the presence orapplication of one or more force fields, for example, magnetic fieldsand electric fields, such as, by induction heating. Thus, the controlledcoating on the surface of the particles provides particularly usefuladvantages in heating applications and in controlling the response ofthe particle and/or particles to the presence or application of one ormore force field. In one embodiment, a flexible heating element isprovided which comprises a flexible matrix material, e.g., an organicpolymeric material in contact with a substrate having an electronicallyconductive tin oxide-containing coating on at least a portion thereof.The coated substrate is adapted and structured as described above.

In addition, an electrostatic dissipation/electromagnetic interferenceshielding element is provided which comprises a three dimensionalsubstrate, e.g., an inorganic substrate, including a porous inorganicsubstrate having an electronically conductive tin oxide-containingcoating on at least a portion of all three dimensions thereof. Thecoated substrate is adapted and structured to provide at least one ofthe following: electrostatic dissipation and electromagneticinterference shielding. As set forth above, one of the preferredapplications for use of the coated porous substrate is in staticdissipation and shielding elements. Thus, the coated porous substratescan have a preferential outer surface coating while limiting the coatingin the internal pore surfaces, such preferen-tial coating effectivelyuses the shielding, static dissipation properties of the outer surfacewhere such outer surfaces in general contribute the major control insuch static dissipation and shielding element applications.

A very useful application for the products of this invention is forstatic, for example, electrostatic, dissipation and shielding,particularly for ceramic and polymeric parts, and more particularly as ameans for effecting static dissipation including controlled staticcharge and dissipation such as used in certain electro static paintingprocesses and/or electric field absorption in parts, such as parts madeof ceramics and polymers and the like, as described herein. The presentproducts can be incorporated directly into the polymer or ceramic and/ora carrier such as a cured or uncured polymer based carrier or otherliquid, as for example in the form of a liquid, paste, hot melt, filmand the like. These product/carrier based materials can be directlyapplied to parts to be treated to improve overall performanceeffectiveness. A heating cycle is generally used to provide for productbonding to the parts. A particular unexpected advantage is the improvedmechanical properties, especially compared to metallic additives whichmay compromise mechanical properties. In addition, the products of thisinvention can be used in molding processes to allow for enhanced staticdissipation and/or shielding properties of polymeric resins relative toan article or device or part without such product or products, and/or tohave a preferential distribution of the product or products at thesurface of the part for greater volume effectiveness within the part.

The particular form of the products, i.e., fibers, flakes, i.e.particles, mats or the like, is chosen based upon the particularrequirements of the part and its application, with one or more offlakes, i.e. platelets, fibers and particles, including spheres, beingpreferred for polymeric parts. In general, it is preferred that theproducts of the invention have a largest dimension, for example, thelength of fiber or particle or side of a flake, of less than about 1/8inch, more preferably less than about 1/64 inch and still morepreferably less than about 1/128 inch. It is preferred that the ratio ofthe longest dimension, for example, length, side or diameter, to theshortest dimension of the products of the present invention be in therange of about 500 to 1 to about 10 to 1, more preferably about 250 to 1to about 25 to 1. The concentration of such product or products in theproduct/carrier and/or mix is preferably less than about 60 weight %,more preferably less than about 40 weight %, and still more preferablyless than about 20 weight %. A particularly useful concentration is thatwhich provides the desired performance while minimizing theconcentration of product in the final article, device or part.

The products of this invention find particular advantage in staticdissipation parts, for example, parts having a surface resistivity inthe range of about 10⁴ ohms/square to about 10¹² ohms/square. Inaddition, those parts generally requiring shielding to a surfaceresistivity in the range of about 1 ohm/square to about 10⁵ ohms/squareand higher find a significant advantage for the above products due totheir mechanical properties and overall improved polymer compatibility,for example, matrix bonding properties as compared to difficult to bondmetal and carbon-based materials. A further advantage of the aboveproducts is their ability to provide static dissipation and/or shieldingin adverse environments such as in corrosive water and/or electrogalvanic environments. As noted above, the products have the ability toabsorb as well as to reflect electro fields. The unique ability of theproducts to absorb allows parts to be designed which can minimize theamount of reflected electro fields that is given off by the part. Thislatter property is particularly important where the reflected fields canadversely affect performance of the part.

A flexible electrostatic dissipation/electro-magnetic interferenceshielding element is also included in the scope of the presentinvention. This flexible element comprises a flexible matrix material,e.g., an organic polymeric material, in contact with a substrate havingan electronically conductive tin oxide-containing coating on at least aportion thereof. The coated substrate of this flexible element isadapted and structured as described above.

The present coating process is particularly suitable for controlling thecomposition and structure of the coating on the substrate to enhance theperformance of the coated substrate in a given, specific application,e.g., a specific resistance heating electrostatic dissipation orelectromagnetic interference shielding application.

The present tin oxide/substrate combinations and matrix material/tinoxide/substrate combinations, which have at least some degree ofporosity, hereinafter referred to as "porous contacting membranes" or"porous membranes", may be employed as active components and/or assupports for active components in systems in which the tinoxide/substrate, e.g., the tin oxide coated substrate, is contacted withone or more other components such as in, for example, separationsystems, gas purification systems, filter medium systems, flocculentsystems and other systems in which the stability and durability of suchcombinations can be advantageously utilized.

Particular applications which combine many of the outstanding propertiesof the products of the present invention include porous and electromembrane separations for gas processing, food processing,textile/leather processing, chemical processing, bio medical processingand water treatment. For example, various types of solutions can befurther concentrated, e.g., latex concentrated, proteins isolated,colloids removed, salts removed, etc. The membranes can be used in flatplate, tubular and/or spiral wound system design. In addition, theproducts of this invention can be used e.g., as polymeric composites,for electromagnetic and electrostatic interference shieldingapplications used for computers, telecommunications and electronicassemblies, as well as in low radar observable systems and staticdissipation, for example, in carpeting and in lightening protectionsystems for aircraft.

Membranes containing voids that are large in comparison with moleculardimensions are considered porous. In these porous membranes, the poresare interconnected, and the membrane may comprise only a few percent ofthe total volume. Transport, whether driven by pressure, concentration,or electrical potential or field, occurs within these pores. Many of thetransport characteristics of porous membranes are determined by the porestructure, with selectivity being governed primarily by the relativesize of the molecules or particles involved in a particular applicationcompared to the membrane pores. Mechanical properties and chemicalresistance are greatly affected by the nature, composition and structuree.g., chemical composition and physical state, of the membrane.

Commercial micropore membranes have pore dimensions, e.g., diameters, inthe range of about 0.005 micron to about 20 microns. They are made froma wide variety of materials in order to provide a range of chemical andsolvent resistances. Some are fiber or fabric reinforced to obtain therequired mechanical rigidity and strength. The operationalcharacteristics of the membrane are defined sometimes in terms of themolecules or particles that will pass through the membrane porestructure.

Microporous membranes are often used as filters. Those with relativelylarge pores are used in separating coarse disperse, suspendedsubstances, such as particulate contamination. Membranes with smallerpores are used for sterile filtration of gases, separation of aerosols,and sterile filtration of pharmaceutical, biological, and heat sensitivesolutions. The very finest membranes may be used to separate, e.g.,purify, soluble macromolecular compounds.

Porous membranes also are used in dialysis applications such a removingwaste from human blood (hemodialysis), for separation of biopolymers,e.g., with molecular weights in the range of about 10,000 to about100,000, and for the analytical measurements of polymer molecularweights. Microporous membranes also may be used as supports for verythin, dense skins or a containers for liquid membranes.

The ability of dense membranes to transport species selectively makespossible molecular separation processes such as desalination of water orgas purification, but with normal thicknesses these rates are extremelyslow. In principle, the membranes could be made thin enough that therates would be attractive, but such thin membranes would be verydifficult to form and to handle, and they would have difficultysupporting the stresses imposed by the application. Conversely,microporous membranes have high transport rates but very poorselectivity for small molecules. Asymmetric membranes, for example madeof the present combinations, in which a very thin, dense membrane isplaced in series with a porous substructure are durable and provide highrates with high selectivity. Such asymmetric membranes and the usethereof are within the scope of the present invention.

Examples of applications for porous membranes include: separation offungal biomass in tertiary oil recovery; concentration of PVC latexdispersions; desalination of sea water; enhancement of catecholaminedetermination; removal of colloids from high purity deionized water;treatment of wool scouring liquids; filtration of tissue homogenates;separation of antigen from antigen-antibody couple in immunoassay;purification of subcutaneous tissue liquid extracts; concentration ofsolubilized proteins and other cellular products; cell debris removal;concentration of microbial suspensions (microbial harvesting); enzymerecovery; hemodialysis; removal of casein, fats and lactose from whey;concentration of albumen; separation of skimmed milk; clarification ofliqueur, fruit juices, sugar, and corn syrup; alcohol fermentation;sterilization of liquids, e.g., beer, wine; continuous microfiltrationof vinegar; concentration and demineralization of cheese, whey, soywhey, vegetable extracts, and flavorings; sugar waste recovery; silverrecovery from photo rinses; dewatering of hazardous wastes; removal ofhydrocarbon oils from waste water; recovery and recycling of sewageeffluent; recovery of dye stuffs from textile mill wastes; recovery ofstarch and proteins from factory waste, wood pulp, and paper processing;separation of water and oil emulsions; separation of carbon dioxide andmethane; and catalytic chemical reactions.

As described above porous membranes can be used in a wide variety ofcontacting systems. In a number of applications, the porous membraneprovides one or more process functions including: filtration,separation, purification, recovery of one or more components, emulsionbreaking, demisting, flocculation, resistance heating and chemicalreaction (catalytic or non- catalytic), e.g., pollutant destruction to anon-hazardous form. The resistance heating and chemical reactionfunctions (applications) set forth herein can be combined with one ormore other functions set forth herein for the porous membranes as wellas such other related porous membrane applications.

The porous membrane, in particular the substrate, can be predominantlyorganic or inorganic, with an inorganic substrate being suitable fordemanding process environments. The porous organic-containing membranesoften include a porous organic based polymer matrix material havingincorporated therein a three dimensional tin oxide-containing material,preferably including an electronically conductive tin dioxide coating,more preferably incorporating a dopant and/or a catalytic species in anamount that provides the desired function, particularly electricalconductivity, without substantially deleteriously affecting theproperties of the organic polymer matrix material. These modifiedpolymer membranes are particularly useful in porous membrane and/orelectromembrane and/or catalytic processes.

Examples of polymer materials useful in microporous membranes includecellulose esters, poly(vinyl chloride), high temperature aromaticpolymers, polytetrafluoroethylene, polymers sold by E. I. DuPontCorporation under the trademark Nation, polyethylene, polypropylene,polystyrene, polyethylene, polycarbonate, nylon, silicone rubber, andasymmetric coated polysulfone fiber.

A very convenient application for the coating process and products ofthis invention is the production of a controlled coating, e.g., a thincoating of tin oxide-containing material, on an inorganic substrate,particularly a porous inorganic substrate, to produce a porous membrane.The process provides a new generation of membranes: porous membranes forcontacting processes, e.g., as described herein. The selectively infiltration, particularly ultra and micro filtration, can also beenhanced by applying an electrical field and/or an electrical potentialto the porous membrane. The electrical field and/or potential can beobtained using a two electrode electrical system, the membrane includinga electronically conductive tin oxide-containing coating constitutingone of the two electrodes (anode or cathode).

Porous multilayer asymmetric electronically conductive inorganicmembranes, produced in accordance with this invention, are particularlyadvantageous for membrane applications. Among the advantages of suchmembranes are: stability at high temperature and/or at large pressuregradients, mechanical stability i.e. reduced and even substantially nocompaction of the membrane under pressure), stability againstmicrobiological attack, chemical stability especially with organicsolvents, steam sterilization at high temperatures, backflush cleaningat pressures of up to 25 atm, and stability in corrosive and oxidationenvironment.

A membrane can be classified as a function of the size of the particles,macromolecules and molecules separated. Micron sized porous ceramics forfiltration processes can be prepared through sintering of appropriatematerials as set forth herein for the manufacture of sensors. However,the preferred process for membrane-based microfiltration,ultrafiltration and reverse osmosis is to provide inorganic layers withultrafine pores and thickness small enough to obtain high flux throughthe membrane, particularly membranes including tin oxide-containingcoatings.

With this type of asymmetric membrane, separation processes are pressuredriven. Another factor is the interaction at the membrane interfacebetween the porous material and the material to be processed. As notedabove, selectivity can be enhanced by applying an electrical field ontothe surface of the membrane. The electrical field is obtained using atwo electrode electrical device; the conductive membrane constitutingone of the two electrodes (anode or cathode--preferably anode). Suchporous membranes can e obtained with one or more electronicallyconductive tin oxide-containing thin layers on a porous substrate.Conductive tin oxide combined with other metal oxide mixtures alsoprovide improved properties for porous membranes and exhibit electronicconductivity, as well as other functions, such as catalysts orresistance heating.

The products of this invention as described herein, are particularlyuseful for resistance heating applications. It has been found that thecoated three dimensional and/or flexible substrates particularly fibers,fiber rovings, chopped fibers, and fiber mats, and flakes and otherparticles can be incorporated into polymeric matrix materials,particularly thermoplastic, thermoset and rubber based polymericmaterials, as describe herein. The tin oxide coated substrates,particularly porous particles can be, for example, E, C, S, or T glass,silica, silica alumina, silica alumina boria, silicon carbide or aluminafibers, rovings, mats, chopped mats, other particles, as set forth aboveetc. What is unexpected is the improved mechanical properties, e.g.,strength coating adhesion and the like, of the coated substratesrelative to the prior art substrates coated using spray pyrolysistechniques and the improved control over coating thickness to matchconductivity requirements for a given resistance heating application.Whereas for many low to moderate temperature applications, organicpolymer matrix materials are preferred, three dimensional productscomprising, preferably primarily comprising flexible or rigid inorganicsubstrates coated with tin oxide-containing coatings have excellent hightemperature performance characteristics useful, for example, in hightemperature resistance heating of liquids and gases, such as air, bycontact with or through (i.e., porous) such three dimensional products.Typical resistance heating applications include: heating elements orunits of electric heating devices, devices for culinary purposes,warming tables, therapeutic heaters, deicing devices such aselectrically heated polymer composites, low-temperature ovens such asdriers, high temperature heating of gases, liquids, etc.

Another very useful application for the products of this invention isfor the joining of parts, particularly polymeric parts, and as a meansfor effecting the sintering or curing of parts, such as ceramics,curable polymers, for example thermoset and rubber based polymers andthe like. The products can be incorporated directly into the polymer orceramic and/or a carrier such as a cured or uncured polymer basedcarrier or other liquid, as for example in the form of a liquid, paste,hot melt, film and the like. These product/carrier based materials canbe directly applied to parts to be joined and resistance heatingparticularly induction heating used to raise the temperature and bondthe parts together at a joint such as through polymer melting and/orcuring. A particular unexpected advantage is the improved mechanicalproperties, especially compared to metallic susceptors which maycompromise mechanical properties. In addition, the products of thisinvention can be used in molding processes to preferentially allow therapid heating and curing of polymeric resins, and/or to have apreferential distribution of the products at the surface of the partsfor subsequent joining of parts. The particular form of the products,i.e., fibers, flakes, spheres, particles, mats or the like, is chosenbased upon the particular requirements of the part and its application,with one or more of flakes, fibers and particles being preferred forjoining or bonding parts. In general, it is preferred that the productsof the invention have a largest dimension, for example the length of afiber or side of a flake, of less than about 1/8 inch, more preferablyless than about 1/64 inch and still more preferably less than about1/128 inch. The concentration of such product or products in theproduct/carrier and/or mix is preferably less than about 50 weight %,more preferably less than about 20 weight %, and still more preferablyless than about 10 weight %. A particularly useful concentration is thatwhich provides the desired heating while minimizing the concentration ofproduct in the final part.

As set forth above, the coated porous substrates are particularly usefulin applications where such coated substrates becomes part of a matrixmaterial, particularly a polymeric matrix material. Thus, for example,the coated substrates can be incorporated into a polymer matrix for usein, for example, bipolar batteries, resistance heating polymer products,porous membranes and shielding dissipation products. In a number of thepreferred applications for use of the coated substrate in polymermatrices, the outer surface coating performs the major intended functionsuch as, for example, surface to surface contact to form an electricalcircuit and/or to be responsive to a force field and/or to reflectand/or absorb a particular wave form such as in shielding applications.In such applications, the internal porosity can reduce the weight of thepolymer matrix product in comparison to a solid, coated particle, and inaddition, the porosity and surface area allows for improved bonding ofthe polymer matrix to the particle. Such polymer matrices containingcoated porous substrates, have improved mechanical structuralproperties, as well as improved properties relating to the functioningof the conductive outer surface of tin oxide.

Another unique application of the present invention combines thestability of the tin oxide containing coating, particularly at hightemperatures and/or in demanding oxidizing environments, with the needto protect a structural element and/or to provide a fluid, i.e., gasand/or liquid, impervious material. Such structural elements aresuitable for use at high temperatures, preferably greater than about400° F., more preferably greater than about 1500° F. or even greaterthan about 2000° F. The present coatings preferably provide protectionagainst oxidation. Examples of structural elements requiring suchprotection and/or a fluid impervious coating include three dimensionalsubstantially carbon or inorganic materials, such as woven ceramicfibers and carbon-carbon composites, useful as turbine enginecomponents, hot air frame components, and hypersonic vehicle structuralelements or components. Due to the fact that carbon oxidizes under thedemands of such environments, barrier or protective coatings arenecessary. A particularly effective barrier coating is a tinoxide-containing coating formed according to the present inventionbecause of the high temperature stability and excellent and completecoverage of such coating.

In addition, it is believed that a layer of at least one lower valenceoxide of tin may form at the carbon tin oxide interface thereby givingadditional barrier protection against excessive carbon oxidation tocarbon oxides gases and decomposition products. The coating process ofthis invention, in addition, can uniformly coat three dimensional wovenstructures, particularly in the vaporous state, to effectively seal offdiffusion of gases and/or liquids between surfaces. For example, ceramicfibers, such as those sold under the trademark Nextel by the 3M Company,can be woven into structures or structural elements, sealed off betweensurfaces, and used in high temperature applications. Such applicationsinclude gas and/or oil radiant and post combustion burner tubes, turbineengine components, and combustion chambers. For the latter, suchstructures can also contain one or more catalytically active materialsthat promote combustion, such as hydrocarbon combustions.

A particularly unique application that relies upon stable electronicconductivity and the physical durability of the products of thisinvention are dispersions of conductive material, such as powders, influids, e.g., water, hydrocarbons, e.g., mineral or synthetic oils,whereby an increase in viscosity, to even solidification, is obtainedwhen an electrical field is applied to the system. These fluids arereferred to as "field dependent" fluids which congeal and which canwithstand forces of shear, tension and compression. These fluids revertto a liquid state when the electric field is turned off. Applicationsinclude dampening, e.g., shock absorbers, variable speed transmissions,clutch mechanisms, etc.

The products of this invention which are particularly useful for formingfield dependent fluids are particulate as set forth above, particularlyporous particulate, particularly as powders. Such particulate can be forexample, spheres, fibers, flakes, i.e. platelets, and such otherparticulates, and powders. Typical examples of such tin oxide coatedparticles are the set forth above under catalysts, resistance heatingand electrostatic and EMI shielding particles. Such particles can haveincorporated therein various dopants to modify conductivity and/or othercomponents can be incorporated for a particular property, includingvarious metal type components. In addition, various inorganic substratesare set forth above which substrates are particularly useful inproducing the particles for use in field dependent fluids.

The coated substrate including the tin dioxide, preferablyelectrorheology electronically conductive tin dioxide, and/oroptionally, electrorheology polarizable tin dioxide and/or at least oneadditional component in an amount effective to promote field dependentfluid performance, is particularly useful as field dependent fluidsincluding electric and magnetic field dependence, particularly electricfield. Preferably the additional component is a polarizable component orconductivity modified in an amount effective to promote such fluidperformance. Thus the promoting effect of the component may be enhancedby the presence of an electrical field in proximity to thecomponent/particle. Thus, the tin dioxide, preferably on a substantiallynon-electronically conductive substrate, eg., a particle, can provide aneffective and efficient electric field dependent fluid, including thosewhich occur or are enhanced when an electric field is applied inproximity to the particle. Thus, it has been found that the presentlycoated substrates are useful as active electrorheological fluidenhancers and as a base modified by additional components that stillfurther enhance electrorheological fluid properties. Without wishing tolimit the invention to any particular theory of operation, it isbelieved that the outstanding stability, e.g., with respect toelectronic properties and/or morphology and/or stability, of the presenttin oxides plays an important role in making useful and effective fielddependent particles, particularly the higher surface area attainable tindioxide particles, particularly when prepared in accordance with thisinvention.

As noted above, it is preferred that the tin oxide particle, tinoxide-containing substrates be electronically conductive and/orpolarizable. Although fluorine doped tin oxide is particularly useful,other dopants may be incorporated in the present particle to provide thetin oxide with the desired electronic and/or polarizable properties. Forexample, antimony may be employed as a tin oxide dopant. Such otherdopants may be incorporated into the final particle, tinoxide-containing coated substrates using one or more processingtechniques substantially analogous to procedures useful to incorporatefluorine dopant, e.g., as described herein.

As set forth above, the tin dioxide particles is present in the fluid inthe amount to enhance the field dependent fluid performance. In additionthe conductivity and/or reciprocal resistivity of the tin dioxideparticle is of a value which promotes the overall performance of thefield dependent fluid, i.e., enhances electrorheological properties ofthe fluid. Typically the resistivity of the tin dioxide particle iswithin the range from about 10⁻³ to about 10⁹ ohm cm, more preferablyfrom about 10¹ to about 10³ ohm cm and still more preferably, from about10 ohm cm to about 10² ohm cm. The conductivity of the tin dioxideparticle can be controlled by the type of dopant, the concentration ofdopant, the processing conditions in order to obtain a resistivitywithin the preferred ranges as set forth above and with improvedelectrorheological modifying properties. In addition to the abovemodifications to obtain a given conductivity other components can beincorporated into the tin oxide coating such as a moderate to highresistance type of material such as silica which produces a tin dioxidecoating having optimized electrorheological properties.

In addition to electrical conductivity as set forth above, thepolarizability of the tin dioxide coating can be modified through theaddition of a component such as to enhance the overall polarizability ofthe tin dioxide particle which enhanced polarizability can improve theoverall electrorheological properties of the fluid. For example, the tindioxide coating can be modified to form surface hydrates which areresponsive to electric fields and produce a reversible change inelectrorheological properties. Other components, particularly polarcomponents, more particularly organic polar components such as surfaceactive agents, alkanol amines such as low molecular weight alkanolamines, alkyl amines and water can in addition be used as polarizationcomponents. Such additional components which alter the polarizationproperties of the tin dioxide coating and can produce field dependentfluids which are useful at elevated temperatures, including for certainfluids use above 70° C. or even above 100° C. The stability anddurability for the present tin oxide materials are believed to make themvery useful in field dependent fluids in more aggressive and/or moreharsh environments, particularly high temperature, and/or pressureand/or oxidation environments.

Certain metal components associated with the tin oxide particle may beemployed, provided that they function to enhance electrorheologicalproperties and/or an application defined property. Among the usefulmetal components are those selected from components of the transitionmetals, the rare earth metals, certain other components and mixturesthereof, in particular, gold, silver, copper, vanadium, chromium, cobaltmolybdenum, tungsten zinc, indium, the platinum group metals, i.e.,platinum, palladium and thorium, iron, nickel, manganese, cesium,titanium, etc. Although metal containing compounds may be employed, itis preferred that the metal components included with the coatedsubstrate comprise elemental metal and/or metal in one or more activeoxidized forms, for example, Cr₂ O₃, Ag₂ O, etc.

The preferred substrate materials include a wide variety of inorganicmaterials including high surface area materials, particularly inorganicoxides and carbon as set forth above, particularly under the catalysts,resistance heating and shielding products of this invention. Additionalsubstrates include for example, alumina, silica, zirconia, magnesia,boria, phosphate, titania, ceria, thoria and the like, as well asmulti-oxide type supports such as alumina-phosphorous oxide, silicaalumina, zeolites, zeolite modified inorganic oxides, e.g., silicaalumina and the like. As set forth above, substrate particle materialscan be in many forms and shapes, especially shapes which are not flatsurfaces, i.e., non line-of-site particulate materials and particularly,spheres. The substrate can be used as is or further processed such as bysintering of powered materials into large aggregates. The aggregates canincorporate other powders, for example, other oxides, to form theaggregates.

As set forth above, the particles include for example, spheres, fibers,flakes, other irregularly shaped geometry such as aggregates and alike.In general the particle size can vary over a wide range, typically aparticle size maximum width of from about 0.04 microns up to a widthrepresenting about 10% of the design gap between electrodes which formthe electric field means associated with the use of the field dependentfluid. More preferably, the range of the width of the particle is fromabout 1 to about 100 microns still more preferably, from about 5 toabout 50 microns. The width of the particles can be adjusted to providevarious degrees of packing densities in the fluid which packingdensities can include a bi-modal type of distribution of particle sizes.

It is preferred that the particles comprise a majority of monoparticles, more preferably, a predominant proportion. The use of monoparticles reduces the tendency of the particles to sheer down to smallersize particles which shear down may accompany the use of particleaggregates in field dependent fluids. In addition, it is preferred tohave a particle aspect ratio, i.e., the maximum particle width dividedby the minimum particle width of less than about 20 to 1, still morepreferably less than about 10 to 1 and still more preferably, less thanabout 5 to 1. One of the preferred shapes is spheres and/or beadswherein the aspect ratio approaches 1 and/or is 1. In practice thespherical particles which are preferred for use in the composition ofthis invention, have a roundness associated with such particlesgenerally greater than about 70%, still more preferably greater thanabout 85% and still more preferably, greater than about 95%.

As set forth above, a particularly preferred particle is a sphericalparticle, particularly spheres within the particle size and roundnessranges set forth above. The spheres can improve overall field dependentfluid performance, particularly in reducing adverse particle effects onthe fluid such as dielectric breakdown. A particularly unique embodimentof the present invention is the use of hollow spheres, particularlywithin the particle size and roundness ranges as set forth above. Suchspheres are hollow i.e. contain one or more closed cell voidshereinafter referred to as hollow spheres and are designed to be densitycompatible with the fluid. The density compatible hollow spheres have adensity in the range of from about 60% to about 140% of the density ofthe fluid, more preferably from about 70% to about 130% of the densityof the fluid, still more preferably from about 80% to about 120% of thedensity of the fluid and still more preferably, from about 90% to about110% of the density of the fluid. Thus, for example, the density of thefluid can vary according to the type of fluid utilized in the fielddependent fluid, such as from about 0.95 g per cc up to about 1.95 g percc for certain chlorinated aromatic fluids. The density compatibility ofthe hollow spheres relates to the particular fluid, including blends offluids utilized as the field dependent fluid. The density compatibilityprovides improved stability of the hollow spheres particulate in thefluid, particularly where settling out the particles can adverselyeffect overall performance of the field dependent fluids and/or wheresuch sedimentation can cause premature failure of the device.

As set forth above, the spheres can be inorganic and for example, carbonand/or inorganic oxide. The preferred inorganic oxides can be forexample alumino silicates, silica, sodium borosilicate, insoluble glass,soda lime glass, soda lime borosilicate glass, silica alumina, as wellas such glasses and ceramics, modified with titanium dioxide and/orsmall amounts of iron oxide. The density of the hollow spheres can bedesigned to be density compatible with the fluid by the density of theinorganic material itself, the hollow and or void volume and thethickness of the wall and the density of surface component on thesphere. For a hollow sphere the aspect ratio, i.e., the diameter of thesphere divided by the thickness of the wall, in part defines both thedensity of the hollow sphere, as well as the buckling pressure of thesphere. Thus as the aspect ratio decreases, the density of the hollowsphere increases and in general, the crush strength of the hollow sphereincreases. Of additional significance is the ability of the hollowsphere under high sheer conditions to provide improved mechanicalstability, particularly at aspect ratios which provide the requisitewall thickness and density compatibility. Thus for example, hollowspheres for use in field dependent fluids can be designed for densitycompatibility at high crush strengths and sheer rates, for example, lessthan about 20% and even less than about 10% breakage at isostaticpressures of greater than 6,000 psi, even up to about 60,000 psi.

As set forth above, the unique hollow spheres having fluid densitycompatibility can be coated with tin dioxide including such additionalcomponents as set forth above. In addition, it has been found that thefluid density designed particles can improve the overall performance ofmaterials that have been shown to exhibit an electrorheological effect.Thus for example, fluid density compatible hollow spheres can have anelectronically conductive and/or polarizable surface componentassociated therewith, including components which are incorporated duringthe processing to produce such fluid density compatible materials. Forexample, alumino silicates, organic polyelectro-lytes, organicpolyampholytes, organic semiconductors, water, polar organic compoundssuch as alcohols, amines, amides, polyhydroxy organic compounds andvarious other surfactant materials which provide a polarizable effect onthe surface can be incorporated on the surface of the hollow sphere.

The surface area can be optimized for the tin oxide coating and/or othercomponents, and/or other conductivity and/or polarizable components, bythe selection of starting materials, porosity forming components andtheir concentration and geometry. Such optimization also takes intoconsideration the final end use application of the substrate. Porositycan also be increased by directly leaching the preformed substratewithin an acid medium, i.e., nitric acid, to selectively remove forexample ceramic constituents for example magnesia and alumina. Suchleaching cannot only increase porosity but also the surface areas of thesubstrate. Typical substrate surface areas can be as set forth above. Inaddition, such ranges can vary from about 0.1 to about 2 meters squareper gram up to about 20 or even up to about 40 or higher meters squareper gram, with the higher areas generally resulting from leached and/orcoated and/or formed porous substrates.

It is generally preferred to have a high surface area in order tooptimize activity for a particular application. As set forth above, thesurface area can be increased by, for example. leaching and/or by theapplication of a surface coating such as a wash-coat which provides fora high surface area surface on the substrate and/or by forming the highsurface area substrate. It is preferred to incorporate other activecomponents as set forth above on a high surface area for improvedoverall effectiveness and activity. As set forth above, it is preferredto have macro pores when a subsequent surface coat is being applied tothe substrate. Such subsequent coatings can include, for example, abarrier coat, a wash coat, and/or the tin oxide coating on the substratesurface.

Other active components may be included with the coated substrate and/orsubstrate using any one or more of various techniques, e.g.,conventional and well known techniques. For example, metal can beincluded with the coated substrate by impregnation; electro-chemicaldeposition; spray hydrolysis; deposition from a molten salt mixture;thermal decomposition of a metal compound or the like. The amount of acomponent included is sufficient to perform the desired functions, andvaries from application to application.

Certain of these and other aspects the present invention are set forthin the following description of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a block flow diagram illustrating a process for producingcertain of the present coated substrates.

DETAILED DESCRIPTION OF THE DRAWING

The following description specifically involves the coating of randomlyoriented, woven mats of C-glass fibers. However, it should be noted thatsubstantially the same process steps can be used to coat other substrateforms and/or materials.

A process system according to the present invention, shown generally at10, includes a preheat section 12, a coating section 14, anequilibration section 16 and an oxidation/sintering section 18. each ofthese sections is in fluid communication with the others. Preferably,each of these sections is a separate processing zone or section.

First gas curtain 20 and second gas curtain 22 provide inert gas,preferably nitrogen, at the points indicated, and, thereby effectivelyinsure that preheat section 12, coating section 14 and equilibriumsection 16 are maintained in a substantially inert environment. Firstexhaust 24 and second exhaust 26 are provided to allow vapors to exit orbe vented from process system 10.

Randomly oriented woven mats of C-glass fibers from substrate source 28is fed to preheat section 12 where the mats are preheated up to amaximum of 375° C. for a time of 1 to 3 minutes at atmospheric pressureto reach thermal equilibrium. These mats are composed of from 8 micronto 35 micron diameter C- or T-glass randomly oriented or woven fibers.The mats are up to 42 inches wide and between 0.058 to 0.174 mil thick.The mats are fed to process system 10 at the rate of about 1 to 5 feetper minute so that the fiber weight through is about 0.141 to about 2.1pounds per minute.

The preheated mats pass to the coating section 14 where the mats arecontacted with an hydrous mixture of 70% to 95% by weight of stannouschloride and 5% to 30% by weight of stannous fluoride from raw materialsource 30. This contacting effects a coating of this mixture on themats.

This contacting may occur in a number of different ways. For example,the SnCl₂ /SnF₂ mixture can be combined with nitrogen to form a vaporwhich is at a temperature of from about 25° C. to about 150° C. higherthan the temperature of the mats in the coating section 14. As thisvapor is brought into contact with the mats, the temperaturedifferential between the mats and the vapor and the amount of themixture in the vapor are such as to cause controlled amounts of SnCl₂and SnF₂ to condense on and coat the mats.

Another approach is to apply the SnCl₂ /SnF₂ mixture in a molten formdirectly to the mats in an inert atmosphere. There are severalalternatives for continuously applying the molten mixture to the mats.Obtaining substantially uniform distribution of the mixture on the matsia a key objective. For example, the mats can be compressed between twofillers that are continuously coated with the molten mixture. Anotheroption is to spray the molten mixture onto the mats. The fiber mats mayalso be dipped directly into the melt. The dipped fiber mats may besubjected to a compression roller step, a vertical lift step and/or avacuum filtration step to remove excess molten mixture from the fibermats.

An additional alternative is to apply the SnCl₂ /SnFn₂ in an organicsolvent. The solvent is then evaporated, leaving a substantially uniformcoating of SnCl₂ /SnF₂ on the fiber mats. The solvent needs to besubstantially none-reactive (at the conditions of the present process)and provide for substantial solubility of SnCl₂ and SnF₂. For example,the dipping solution involved should preferably be at least about 0.1molar in SnCl₂ /SnF₂. Substantially anhydrous solvents comprisingacetonitrile, ethyl acetate, dimethyl sulfoxide, propylene carbonate andmixtures thereof are suitable. Stannous fluoride is often less solublein organic solvents than is stannous chloride. One approach toovercoming this relative insolubility of SnF₂ is to introduce SnF₂ ontothe fiber mats after the fiber mats are dipped into the SnCl₂ solutionwith organic solvent. Although the dopant may be introduced in thesintering section 18, it is preferred to incorporate the dopant in thecoating section 14 or the equilibration section 16, more preferably thecoating section 14.

Any part of process system 10 that is exposed to SnCl₂ and/or SnF₂ meltor vapor is preferably corrosion resistant, more preferably lined withinert refractory material.

In any event, the mats in the coating section 14 are at a temperature ofup to about 375° C., and this section is operated at slightly less thanatmospheric pressure. If the SnCl₂ /SnF₂ coating is applied as a moltenmelt between compression rollers, it is preferred that such compressionrollers remain in contact with the fiber mats for about 0.1 to about 2minutes, more preferably about 1 to about 2 minutes.

After the SnCl₂ /SnF₂ coating is applied to the fiber mats, the fibermats are passed to the equilibration section 16. Here, the coated fibermats are maintained, preferably at a higher temperature than in coatingsection 14, in a substantially inert atmosphere for a period of time,preferably up to about 10 minutes, to allow the coating to moreuniformly distribute over the fibers. In addition, if the fluorinecomponent is introduced onto the fiber mats separate from the stannouschloride, the time the coated fiber mats spend in the equilibrationsection 16 results in the dopant component becoming more uniformlydispersed or distributed throughout the stannous chloride coating.Further, it is preferred that any vapor and/or liquid which separatefrom the coated fiber mats in the equilibration section 16 betransferred back and used in the coating section 14. This preferredoption, illustrated schematically in FIG. 1 by lines 32 (for the vapor)and 34 (for the liquid) increases the effective overall utilization ofSnCl₂ and SnF₂ in the process so that losses of these components, aswell as other materials such as solvents, are reduced.

The coated fiber mats are passed from the equilibration zone 16 into thesintering zone 18 where such fiber mats are contacted with an oxidizer,such as an oxygen-containing gas, from line 36. The oxidizer preferablycomprises a mixture of air and water vapor. This mixture, whichpreferably includes about 1% to about 50% m more preferably about 15% toabout 35%, by weight of water, is contacted with the coated fiber matsat atmospheric pressure at a temperature of about 400° C. to about 550°C. for up to about 10 minutes. Such contacting results in converting thecoating on the fiber mats to a fluorine doped tin dioxide coating. Thefluorine doped tin oxide coated fiber mats product, which exitssintering section 18 via line 38, has useful electric conductivityproperties. This product preferably has a doped tin oxide coating havinga thickness in the range of about 0.5 microns to about 1 micron, and isparticularly useful as a component in a lead-acid battery. Preferably,the product is substantially free of metals contamination which isdetrimental to electrical conductivity.

The present process provides substantial benefits. For example, theproduct obtained has a fluorine doped tin oxide coating which has usefulproperties, e.g., outstanding electrical and/or morphologicalproperties. This product may be employed in a lead-acid battery or incombination with a metallic catalyst to promote chemical reactions,e.g., chemical reductions, or alone or in combination with a metallicsensing component to provide sensors, e.g., gas sensors. Highutilization of stannous chloride and fluorine components is achieved. Inaddition, high coating deposition and product throughout rates areobtained. Moreover, relatively mild conditions are employed. Forexample, temperatures within sintering section 19 can be significantlyless than 600° C. The product obtained has excellent stability anddurability.

EXAMPLE 1

A randomly oriented mat substrate made of C-glass was contacted with amolten mixture containing 30 mol % SnF₂ and 70 mol % SnCl₂. Thiscontacting occurred at 350° C. in an argon atmosphere at aboutatmospheric pressure and resulted in a coating containing SnCl₂ and SnF₂being placed on the substrate.

This coated substrate was then heated to 375° C. and allowed to stand inan argon atmosphere at about atmospheric pressure for about 5 minutes.The coated substrate was then fired at 500° C. for 20 minutes usingflowing, at the rate of one (1) liter per minute, water saturated air atabout atmospheric pressure. This resulted in a substrate having afluorine doped tin oxide coating with excellent electronic properties.For example, the volume resistivity of this material was determined tobe 7.5×10⁻⁴ ohm-cm.

In the previously noted publication "Preparation of Thick CrystallineFilms of Tin Oxide and Porous Glass Partially Filled with Tin Oxide," anattempt to produce antimony doped tin oxide films on a 96% silica glasssubstrate involving stannous chloride oxidation at anhydrous conditionsresulted in a material having a volume resistivity of 1.5×10⁻⁷ ohm-cm.

The present methods and products, illustrated above, provide outstandingadvantages. For example, the fluorine doped tin oxide coated substrateprepared in accordance with the present invention has improved, i.e.,reduced, electronic resistivity, relative to substrates produced byprior methods.

EXAMPLE 2

Stannous chloride powder is applied to a 26 inches by 26 inch glassfiber non woven mat in the form of a powder (10 to 125 microns inaverage particle diameter) shaken from a powder spreading apparatuspositioned 2 to about 5 feet above the mat. An amount of stannousfluorine powder (10 to about 125 microns in average particle diameter)is added directly to the stannous chloride powder to provide fluoridedopant for the final tin oxide product. The preferred range to achievelow resistance tin oxide products is about 15% to about 20% by weight ofstannous fluoride, based on the total weight of the powder. Thepowder-containing mat is placed into a coating furnace chamber at 350°C. and maintained at this temperature for approximately 20 minutes.During this time a downflow of 9.0 liters per minute of nitrogen heatedto 350° C. to 350° C. is maintained in the chamber.

In the coating chamber the stannous chloride powder melts and wicksalong the fiber to from a uniform coating. In addition, a small cloud ofstannous chloride vapor can form above the mat. This is due to a smallrefluxing action in which hot stannous chloride vapors rise slightly andare then forced back down into the mat for coating and distribution bythe nitrogen downflow. This wicking and/or refluxing is believed to aidin the uniform distribution of stannous chloride in the coating chamber.

The mat is then moved into the oxidation chamber. The oxidation stepoccurs in a molecular oxygen-containing atmosphere at a temperature of525° C. for a period of time of 10 to 20 minutes. The mat may be coatedby this process more than once to achieve thicker coatings.

EXAMPLE 3

Example 2 is repeated except that the powder is applied to the mat usinga powder sprayer which includes a canister for fluidizing the powder andprovides for direct injection of the powder into a spray gun. The powderis then sprayed directly on the mat, resulting in a highly uniformpowder distribution.

EXAMPLE 4

Example 2 is repeated except that the powder is applied to the mat bypulling the mat through a fluidized bed of the powder, which is anaverage particle diameter of about 5 to about 125 microns.

EXAMPLE 5 to 7

Examples 2, 3 and 4 are repeated except that, prior to contacting withthe powder, the mat is charged by passing electrostatically charged airover the mat. The powder particles are charged with an opposite chargeto that of the mat. The use of oppositely charged mat and powder acts toassist or enhance the adherence of the powder to the mat.

EXAMPLES 8 TO 13

Examples 2 to 7 are repeated except that no stannous fluoride isincluded in the powder. Instead, hydrogen fluoride gas is included inthe downflow nitrogen gas in the chamber. The preferred weight ratio oftin to fluoride fed to the chamber to achieve low resistance tin oxideproducts is in the range of about 0.05 to about 0.2.

EXAMPLES 14 TO 16

Examples 3, 6, and 9 are repeated except that an alumina poroussubstrate having an average particle thickness of 120 microns isincorporated into the powder composition at a concentration of about 30wt %. Prior to processing the mat in the equilibration and oxidationsection of the reactor, a second mat was placed underneath the coatedmat. The temperature of the equilibration section of the reactor was at450° C. and the oxidation section was at 550° C. The atmospheres in eachsection are as set forth in Example 1. The powder coated poroussubstrate and top and bottom mats is moved into the equilibrationsection for a time of about 5-20 seconds. The powder melts on the outersurfaces of the porous substrate with controlled coating in the macropores of the porous substrate. The particles and mats are transferredrapidly to the oxidation section, i.e. less than 1 second and the matsand coated substrates are contacted with the oxygen water/vapor mixture.After processing the particulate material incorporated as part of thepowder is removed from the top and bottom mats and is found to have athin, less than 0.3 micron, uniform coatings of tin dioxide on thecomplete particle surface.

EXAMPLE 17

Example 14 is repeated except that a porous silica bead having a beaddiameter of 90 microns, a surface area of 440M² /g, a pore volume of 3.1(cc/g) and a pore diameter of 280 angstroms is substituted for theporous alumina substrate.

EXAMPLE 18

Example 17 is repeated except that a porous silica extrudate having aparticle size of 1/64", a surface area of 300M² /g, a pore volume of 1.0cc/g and a pore diameter of 133 angstroms is substituted for the silicabead.

In each of the Examples 2 to 19, the final coated product includes aneffectively fluoride doped tin oxide-containing outside surface coatinghaving a substantial degree of uniformity and a limited coating on theinternal pore surfaces.

The above examples set forth the significant process and productsadvancements through the practice of this invention. The followingexamples and processing results as set forth were obtained when asubstrate mat of example 1 was substituted in state of the art equipmentused for the processing of flat types of substrate, particularly flatglass.

EXAMPLE 19

Example 17 is repeated except that a porous alumina substrate having amean macro pore size of 45 microns, an apparent porosity of 59%, asurface area of 0.3M² /g and a bulk density of 1.4 is substituted forthe silica substrate.

EXAMPLE 20

A commercial spray pyrolysis process unit was used to compare theprocessing of a flat glass soda lime substrate with the processing of anon-woven porous mat of the type set forth in example 1. The spraypyrolysis unit had a process capability to coat a flat glass having adimension of from 3 feet in width to 5 feet in length. In the unit asolution composition was atomized and sprayed directly at the surface.The temperature of the substrate was obtained by placing the substratewithin an electrically heated furnace. The substrate was then removedfrom the furnace and immediately contacted with the atomized solutionspray. The deposition parameters were as follows: temperature 500° C.,gas delivery pressure solution 30 psi, compressed air 40-60 psi, sprayconfiguration--round spray, vertical deposition, final coatdistance--16" to 18", solution feed rate--5-20 ml per minute, sprayingtime 30-60 seconds. The spray solution contained 50% stannic chloride,deionized water, methanol and hydrofluoric acid (48 wt %) in a ratio ofabout 1 to 1 to 1 to 0.1. The following results were obtained from theprocessing of a flat soda lime glass, and a non-woven C glass mat havinga thickness of about 0.65", a dimension of 16"×16" and a bulk porosityof about 90%. Each substrate was processed according to the aboveconditions and after processing it was determined that the flat glasshad a resistivity of 10 ohms per square while the C glass mat had noevidence of a coating. The process was repeated except that that mat wasplaced in front of the flat glass. After processing, there was noevidence of coating on the C glass mat. However, the backside flat glasshad a conductive coating. Following the failure to coat the glass mat,using state of the art, spray pyrolysis technology, the process unit wasmodified by placing a 1" thick stainless steel plate on which tovertically mount the C glass mat. The mat after processing with the 1"stainless steel backing produced a resistivity of 600-800 ohms persquare on the inner surface of the mat. The process unit was againmodified to place mesh screens over the front of the mat, accompanied bybolting of the screens to the back of the stainless steel plate. Theresults of the combination of steel plate and mesh plate over the frontof the mat was a mat conductivity of 5-6 ohms per square. However, themesh plate obstructed the contact of the spray solution with the meshunderlying portions of the glass mat. In order to achieve a conductivityof 5-6 ohms per square, 20 coatings on both the front and back sideswere required. The modifications made to the state of the art processunit, were not available in the prior art.

EXAMPLE 21

A horizontal continuous chemical vapor deposition (CVD) furnacemanufactured by Watkins-Johnson was evaluated for the coating of thenon-woven fabric of Example 1. The furnace is described in CircuitsManufacturing, October 1975. The furnace differs from the spraypyrolysis system of Example 19 by the continuous nature of the furnaceand the use of vapor deposition of reactants. The furnace temperaturecould be profiled to reach approximately 560° C. and has been used toproduce tin dioxide coated flat glass in one pass. The CVD furnace usedtetramethyl tin, or stannic chloride as the vaporous tin source. Thefluoride dopant source used with tetramethyl tin was trifluoro- bromomethane and with stannic chloride was hydro- fluoric acid. The oxidantin the CVD furnace was a combination of water (vapor) and methanal. Thenon-woven mat used to evaluate the state of the art process equipment,was the same non-woven mat used in Examples 1 and 18. The process wasevaluated using the highest temperature attainable in the oven using theslowest belt speed and at conditions to maximize reactant deposition andformation of a fluoride doped tin dioxide. A series of 25 process runswere made in the furnace and it was determined that essentially nodeposition and coating was obtained on the non-woven mat. The sameconditions with flat glass produced highly conductive tin dioxidecoatings on soda lime glass.

EXAMPLE 22

An electrolysis tin oxide deposition method that had been usedexperimentally on flat surfaces was evaluated for coating non-woven matof the type set forth in examples 1, 20 and 21. The method was based onthe controlled homogenous precipitation of tin hydrate hydroxide from anaqueous solution of stannic chloride complexed with ammonium chloride.In the method, a catalyst (silver nitrate) is added in order to initiateprecipitation. Precipitation begins when the substrate is immersed andthe pH is brought up to 7.5 with sodium hydroxide. The results obtainedwhen a non-woven fabric was utilized in the process were very lowdeposition rates, poor materials utilization, poor coating adhesion,poor fiber coating, i.e., clumps, poor continuity of the fiber, very lowto zero dopant incorporation and a very high resistivity tin oxide.

The results set forth in examples 20, 21 and 22 demonstrate thedifficult and substantial problems associated with the coating ofshielded surfaces and/or 3-D type substrates. In examples 20 and 21, thesubstitution of a 3-dimensional, non-woven fabric for a flat glasssubstrate in units which are used to effectively coat flat glass wereunsuccessful in their application to a 3-dimensional substrates and/orsubstrates with shielded surfaces. In addition, example 22 demonstratesthe difficulty in processing 3-D substrates, i.e., very high resistivityand in addition, the difficult problem of incorporation of a dopant toprovide enhanced electrical conductivity. A comparison between example 1and examples 20, 21 and 22 demonstrate the unexpected, unique advantagesand advances of the processes of this invention and the unique productsfor use in a wide variety of applications.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

What is claimed is:
 1. An article comprising a three dimensionalinorganic, porous substrate other than electrically conductive tin oxidehaving an outer surface area and an internal pore surface area andhaving a coating containing electrically conductive tin oxide on atleast a majority portion of the outer surface area of all threedimensions thereof and a limited coating of at least about 10 percentnon coated internal pore surface area of said substrate, said poroussubstrate having a total surface area of from about 0.01 to about 700 m²/gram.
 2. The article of claim 1 wherein the substrate is selected fromthe group consisting of silicon carbide and an inorganic oxide.
 3. Thearticle of claim 2 wherein the substrate is an inorganic oxide.
 4. Thearticle of claim 3 wherein said coating includes an effective amount ofa dopant.
 5. The article of claim 4 wherein the dopant is fluoride. 6.The article of claim 1 wherein said coating has a thickness in the rangeof from about 0.1 micron to about 10 microns.
 7. The article of claim 1which further comprises an organic polymeric matrix material in contactwith said coated substrate.
 8. The article of claim 3 wherein theinorganic oxide is selected from the group consisting of alumina,silica, zirconia, titania, silica alumina, a zeolite, boria, zeolitemodified inorganic oxide, alumina phosphorus oxide, zirconium silicate,magnesia, a perovskite, a spinel, an aluminate and mixtures thereof. 9.The article of claim 4 wherein the inorganic oxide is selected from thegroup consisting of alumina, silica, silica alumina, zeolite modifiedinorganic oxide, titania, and mixtures thereof.
 10. The article of claim5 wherein the inorganic oxide is selected from the group consisting ofalumina, silica, silica alumina, zeolite modified inorganic oxide,titania and mixtures thereof.
 11. The article of claim 1 wherein thecoating containing tin oxide is on at least about 70% of the outersurface of all three dimensions thereof and at least about 10% of theinternal pore surfaces are non-coated.
 12. The article of claim 1wherein the pore substrate has a bulk density of from about 10% to about70%.
 13. The article of claim 4 wherein the pore substrate has a bulkdensity of from about 10% to about 70%.
 14. The article of claim 9wherein the pore substrate has a bulk density of from about 10% to about70%.
 15. The article of claim 7 wherein the polymeric matrix material isselected from the group consisting of a polyolefin, a polyvinyl polymer,an epoxy-based polymer, a phenol-formaldehyde polymer, a polyester, apolyvinyl ester, a polyurethane and mixtures thereof.
 16. The article ofclaim 1 which further comprises a lead oxide positive active electrodematerial in contact with said coated substrate and said porous substrateis an acid resistant particle.
 17. The article of claim 1 wherein thesurface area of the porous substrate is from about 10 to about 600 m²/gram, and said porous substrate has a porosity having at least one ofthe following physical properties: a bulk density of from about 10% toabout 70% or a pore volume of from about 0.4 cc/gram to about 3.5cc/gram.
 18. The article of claim 1 wherein the porous substrate is aparticle selected from the group consisting of a pellet, an extrudate, abead, a flake, an aggregate, a ring, a saddle, and a star.
 19. Thearticle of claim 8 wherein the porous substrate is a particle selectedfrom the group consisting of a pellet, an extrudate, a bead, a flake, anaggregate, a ring, a saddle, and a star.
 20. The article of claim 1which further comprises a catalyst material associated with said poroussubstrate.
 21. The article of claim 8 which further comprises a catalystmaterial associated with said porous substrate.
 22. The article of claim18 which further comprises a catalyst material associated with saidporous substrate and the coating containing tin oxide is on at leastabout 70% of the outer surface of all three dimensions thereof and atleast about 10% of the internal pore surfaces are non coated.
 23. Thearticle of claim 21 wherein said catalyst material includes at least onemetal selected from the group consisting of gold, silver, copper,vanadium, chromium, tungsten, zinc, indium, antimony, a platinum groupmetal, iron, nickel, manganese, cesium, and titanium.
 24. The article ofclaim 23 wherein said coating includes an effective amount of a dopantand the dopant is fluoride.